build(ci): make build-guests run on pr to master

Author: mise42

.github/workflows/build.yml

@@ -123,11 +123,12 @@ jobs:
   # Generate guest program list dynamically
   generate-guest-matrix:
     runs-on: ubuntu-latest
-    # Run on main branches, release branches, or when explicitly requested
+    # Run on main branches, release branches, PRs to master, or when explicitly requested
     if: |
       github.ref == 'refs/heads/master' ||
       startsWith(github.ref, 'refs/heads/release/') ||
       startsWith(github.ref, 'refs/tags/v') ||
+      github.base_ref == 'master' ||
       contains(github.event.pull_request.labels.*.name, 'full-build')
     outputs:
       guest-matrix: ${{ steps.generate-matrix.outputs.guest-matrix }}
@@ -189,7 +190,7 @@ jobs:
   collect-guests:
     runs-on: ubuntu-latest
     needs: [generate-guest-matrix, build-guest]
-    if: github.event_name == 'push' || contains(github.event.pull_request.labels.*.name, 'full-build')
+    if: github.event_name == 'push' || github.base_ref == 'master' || contains(github.event.pull_request.labels.*.name, 'full-build')
     steps:
       - name: Download all guest artifacts
         uses: actions/download-artifact@v4