ci(audience): restore PlayMode cells via set-matrix helper job (SDK-330)

- Replaces the cross-product matrix (unity x target x backend with
  axis-matching include items) with a `set-matrix` helper job that emits
  a fully-specified JSON matrix.
- The cross-product approach silently expanded to zero playmode cells
  on every run since SDK-327, so Windows and macOS PlayMode tests have
  not actually run on PRs (verified on the SDK-327 merge commit and on
  PR #748).
- `set-matrix` runs on ubuntu-latest, defines the full 12-cell matrix
  inline as JSON, and uses jq to strip Unity 2022.3.62f2 cells when the
  trigger is pull_request. Schedule and workflow_dispatch get all 12.
- `playmode` declares `needs: set-matrix` and consumes the JSON via
  `matrix.include: fromJSON(needs.set-matrix.outputs.playmode)`.
- Each cell in the JSON carries every key the steps need (target,
  backend, unity, changeset, runner), so there is no axis-match
  augmentation step that can silently drop keys.
- mobile-build job and steps unchanged in this PR; mobile-build trigger
  fix lives in SDK-329 and rebases on top.

Linear: https://linear.app/imtbl/issue/SDK-330

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: ImmutableJeffrey

.github/workflows/test-audience-sample-app.yml

@@ -26,11 +26,41 @@ concurrency:
   cancel-in-progress: true
 
 jobs:
-  # Reduced matrix on pull_request, full matrix on schedule and
-  # workflow_dispatch. The self-hosted Windows runner pool is small, so
-  # trimming PR cells keeps PR feedback fast. `matrix.exclude` below is
-  # the source of truth for which cells are dropped on pull_request.
+  # The PlayMode matrix is built by `set-matrix` below and consumed by
+  # `playmode` via fromJSON. PR runs trim Unity 2022.3.62f2 cells (so 8
+  # of 12 run) to keep the self-hosted Windows runner pool serving PR
+  # feedback fast; schedule and workflow_dispatch run the full 12.
+  set-matrix:
+    runs-on: ubuntu-latest
+    outputs:
+      playmode: ${{ steps.set.outputs.playmode }}
+    steps:
+      - id: set
+        shell: bash
+        run: |
+          full='[
+            {"target":"StandaloneWindows64","backend":"IL2CPP","unity":"2021.3.45f2","changeset":"88f88f591b2e","runner":["self-hosted","Windows","X64"]},
+            {"target":"StandaloneWindows64","backend":"Mono2x","unity":"2021.3.45f2","changeset":"88f88f591b2e","runner":["self-hosted","Windows","X64"]},
+            {"target":"StandaloneOSX","backend":"IL2CPP","unity":"2021.3.45f2","changeset":"88f88f591b2e","runner":["self-hosted","macOS","ARM64"]},
+            {"target":"StandaloneOSX","backend":"Mono2x","unity":"2021.3.45f2","changeset":"88f88f591b2e","runner":["self-hosted","macOS","ARM64"]},
+            {"target":"StandaloneWindows64","backend":"IL2CPP","unity":"6000.4.0f1","changeset":"8cf496087c8f","runner":["self-hosted","Windows","X64"]},
+            {"target":"StandaloneWindows64","backend":"Mono2x","unity":"6000.4.0f1","changeset":"8cf496087c8f","runner":["self-hosted","Windows","X64"]},
+            {"target":"StandaloneOSX","backend":"IL2CPP","unity":"6000.4.0f1","changeset":"8cf496087c8f","runner":["self-hosted","macOS","ARM64"]},
+            {"target":"StandaloneOSX","backend":"Mono2x","unity":"6000.4.0f1","changeset":"8cf496087c8f","runner":["self-hosted","macOS","ARM64"]},
+            {"target":"StandaloneWindows64","backend":"IL2CPP","unity":"2022.3.62f2","changeset":"7670c08855a9","runner":["self-hosted","Windows","X64"]},
+            {"target":"StandaloneWindows64","backend":"Mono2x","unity":"2022.3.62f2","changeset":"7670c08855a9","runner":["self-hosted","Windows","X64"]},
+            {"target":"StandaloneOSX","backend":"IL2CPP","unity":"2022.3.62f2","changeset":"7670c08855a9","runner":["self-hosted","macOS","ARM64"]},
+            {"target":"StandaloneOSX","backend":"Mono2x","unity":"2022.3.62f2","changeset":"7670c08855a9","runner":["self-hosted","macOS","ARM64"]}
+          ]'
+          if [[ "${{ github.event_name }}" == "pull_request" ]]; then
+            matrix=$(jq -c '[.[] | select(.unity != "2022.3.62f2")]' <<<"$full")
+          else
+            matrix=$(jq -c '.' <<<"$full")
+          fi
+          echo "playmode=$matrix" >> "$GITHUB_OUTPUT"
+
   playmode:
+    needs: set-matrix
     if: |
       (github.event_name == 'pull_request' && github.event.pull_request.head.repo.fork == false)
       || github.event_name == 'schedule'
@@ -39,21 +69,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        unity: ['2021.3.45f2', '6000.4.0f1', '2022.3.62f2']
-        target: [StandaloneWindows64, StandaloneOSX]
-        backend: [IL2CPP, Mono2x]
-        include:
-          - unity: '2021.3.45f2'
-            changeset: 88f88f591b2e
-          - unity: '6000.4.0f1'
-            changeset: 8cf496087c8f
-          - unity: '2022.3.62f2'
-            changeset: 7670c08855a9
-          - target: StandaloneWindows64
-            runner: [self-hosted, Windows, X64]
-          - target: StandaloneOSX
-            runner: [self-hosted, macOS, ARM64]
-        exclude: ${{ fromJSON(github.event_name == 'pull_request' && '[{"unity":"2022.3.62f2"}]' || '[]') }}
+        include: ${{ fromJSON(needs.set-matrix.outputs.playmode) }}
     runs-on: ${{ matrix.runner }}
     # Healthy cells finish in ~10 min. 30 min covers cold caches +
     # IL2CPP + Unity 6 startup; anything past that is a hang. Capping