chore(java-spanner): migrate and adapt GitHub Actions workflows

Author: chingor13

…/integration-tests-against-emulator.yaml …-integration-tests-against-emulator.yamljava-spanner/.github/workflows/integration-tests-against-emulator.yaml renamed to .github/workflows/java-spanner-integration-tests-against-emulator.yaml java-spanner/.github/workflows/integration-tests-against-emulator.yaml renamed to .github/workflows/java-spanner-integration-tests-against-emulator.yaml

@@ -3,9 +3,25 @@ on:
     branches:
     - main
   pull_request:
-name: integration-tests-against-emulator
+name: java-spanner integration-tests-against-emulator
+env:
+  BUILD_SUBDIR: java-spanner
 jobs:
+  filter:
+    runs-on: ubuntu-latest
+    outputs:
+      library: ${{ steps.filter.outputs.library }}
+    steps:
+    - uses: actions/checkout@v4
+    - uses: dorny/paths-filter@v3
+      id: filter
+      with:
+        filters: |
+          library:
+            - 'java-spanner/**'
   units:
+    needs: filter
+    if: ${{ needs.filter.outputs.library == 'true' }}
     runs-on: ubuntu-latest
 
     services: