Run a do-nothing CI job for documentation changes

Closes shader-slang#5689

.github/workflows/ci.yml

@@ -11,17 +11,39 @@ on:
       - "README.md"
   pull_request:
     branches: [master]
-    paths-ignore:
-      - "docs/**"
-      - "LICENSES/**"
-      - "LICENSE"
-      - "CONTRIBUTING.md"
-      - "README.md"
 concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}
   cancel-in-progress: true
 jobs:
+  # Because this is a required job, we don't want to not run it for only
+  # documentation changes, so perform the check here rather than at the
+  # meta-level
+  paths-filter:
+    runs-on: ubuntu-latest
+    outputs:
+      should-run: ${{ steps.filter.outputs.should-run }}
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+      - id: filter
+        run: |
+          if [[ "${{ github.event_name }}" == "pull_request" ]]; then
+            git fetch origin ${{ github.base_ref }}
+            if git diff --name-only -z origin/${{ github.base_ref }}...HEAD | 
+              grep --null-data -qvE '^(docs/|LICENSES/|LICENSE$|CONTRIBUTING\.md$|README\.md$)'; then
+              echo "should-run=true" >> $GITHUB_OUTPUT
+            else
+              echo "should-run=false" >> $GITHUB_OUTPUT
+            fi
+          else
+            # For pushes, always run
+            echo "should-run=true" >> $GITHUB_OUTPUT
+          fi
+
   build:
+    needs: paths-filter
+    if: github.event_name == 'push' || needs.paths-filter.outputs.should-run == 'true'
     strategy:
       matrix:
         os: [linux, macos, windows]