ci: ensure backend update PRs trigger CI (#1158)

Co-authored-by: MilesCranmerBot <milescranmerbot@users.noreply.github.com>
Co-authored-by: Miles Cranmer <miles.cranmer@gmail.com>

Author: MilesCranmerBot

.github/workflows/CI.yml

@@ -14,6 +14,8 @@ on:
     paths:
       - '**'
 
+  workflow_dispatch:
+
 permissions:
   contents: write
 

.github/workflows/CI_Windows.yml

@@ -14,6 +14,8 @@ on:
     paths:
       - '**'
 
+  workflow_dispatch:
+
 jobs:
   test:
     runs-on: ${{ matrix.os }}

.github/workflows/CI_mac.yml

@@ -14,6 +14,8 @@ on:
     paths:
       - '**'
 
+  workflow_dispatch:
+
 jobs:
   test:
     runs-on: ${{ matrix.os }}

.github/workflows/update_backend.yml

@@ -3,6 +3,12 @@ on:
   schedule:
     - cron: '00 00 * * *'
   workflow_dispatch:
+
+permissions:
+  contents: write
+  pull-requests: write
+  actions: write
+
 jobs:
   update_compat:
     runs-on: ubuntu-latest
@@ -38,6 +44,7 @@ jobs:
           fi
 
       - name: "Create PR if necessary"
+        id: cpr
         uses: peter-evans/create-pull-request@v8
         with:
           branch: backend-update/v${{ steps.get-latest.outputs.version }}
@@ -51,3 +58,13 @@ jobs:
           add-paths: |
             pyproject.toml
             pysr/juliapkg.json
+
+      - name: "Trigger CI workflows (backend update PR)"
+        if: steps.cpr.outputs.pull-request-number != ''
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: |
+          ref="backend-update/v${{ steps.get-latest.outputs.version }}"
+          gh workflow run "Linux" --repo "$GITHUB_REPOSITORY" --ref "$ref" || true
+          gh workflow run "macOS" --repo "$GITHUB_REPOSITORY" --ref "$ref" || true
+          gh workflow run "Windows" --repo "$GITHUB_REPOSITORY" --ref "$ref" || true