ci: handle packageManager field in plugin-ci to avoid pnpm version conflict

pnpm/action-setup@v4 errors when both the `version` input and a
`packageManager` field in package.json are specified. Detect the
packageManager field during the package-manager detection step and
conditionally omit `version: latest` when it is present.

Fixes CI failures on repos using Corepack-style pnpm version pinning
(e.g. headlamp-polaris-plugin PR #103).

Co-Authored-By: Paperclip <noreply@paperclip.ing>

.github/workflows/plugin-ci.yaml

@@ -23,12 +23,24 @@ jobs:
         run: |
           if [ -f "pnpm-lock.yaml" ]; then
             echo "manager=pnpm" >> $GITHUB_OUTPUT
+            # Check for packageManager field in package.json (Corepack pinning).
+            # pnpm/action-setup@v4 errors if both `version` input and `packageManager`
+            # are set, so we detect here and use two conditional steps below.
+            PM=$(node -e "try{const p=require('./package.json');const v=p.packageManager||'';console.log(v.startsWith('pnpm@')?'true':'false')}catch(e){console.log('false')}" 2>/dev/null || echo "false")
+            echo "has_package_manager=$PM" >> $GITHUB_OUTPUT
           else
             echo "manager=npm" >> $GITHUB_OUTPUT
+            echo "has_package_manager=false" >> $GITHUB_OUTPUT
           fi
 
-      - name: Setup pnpm
-        if: steps.pkg-manager.outputs.manager == 'pnpm'
+      - name: Setup pnpm (version from packageManager field)
+        if: steps.pkg-manager.outputs.manager == 'pnpm' && steps.pkg-manager.outputs.has_package_manager == 'true'
+        uses: pnpm/action-setup@v4
+        with:
+          run_install: false
+
+      - name: Setup pnpm (version latest)
+        if: steps.pkg-manager.outputs.manager == 'pnpm' && steps.pkg-manager.outputs.has_package_manager == 'false'
         uses: pnpm/action-setup@v4
         with:
           run_install: false