CI: Only test default deployment.yaml in forks

For concrete instances of the admin guide we don't need to test all
permutations, only the actual config.

Author: markgoddard

.github/workflows/pull_request.yml

@@ -3,16 +3,29 @@ name: Build OpenStack admin guide
 on: 
   - pull_request
 jobs:
+  # Dynamically define test matrix.
+  # In openstack-admin-guide CI we want to test various configurations.
+  # In client admin guide CI we just want to test the actual configuration.
+  # https://stackoverflow.com/questions/65384420/how-do-i-make-a-github-action-matrix-element-conditional
+  matrix:
+    name: Generate test matrix
+    runs-on: ubuntu-latest
+    outputs:
+      matrix: ${{ steps.set-matrix.outputs.matrix }}
+    steps:
+      # TODO:
+      # if ${{ github.repository }} == 'stackhpc/openstack-admin-guide'
+      - name: Generate test matrix
+        id: set-matrix
+        run: |
+          echo "matrix={\"deployment_yaml\":[\"__default__\",\"disable-ceph\",\"enable-ironic\",\"enable-ironic-no-cleaning-or-physnet\"]}" >> $GITHUB_OUTPUT
+
   build:
     name: Build OpenStack admin guide
+    needs: matrix
     runs-on: ubuntu-latest
     strategy:
-      matrix:
-        deployment_yaml:
-          - __default__
-          - disable-ceph
-          - enable-ironic
-          - enable-ironic-no-cleaning-or-physnet
+      matrix: ${{ fromJson(needs.matrix.outputs.matrix) }}
     steps:
       - uses: actions/checkout@v3