Fix default application credentials integration test case

Author: C0urante

.github/workflows/pull_request.yml

@@ -29,10 +29,15 @@ jobs:
       - name: Unit tests (Maven)
         run: mvn --batch-mode test
       - name: Integration tests (Maven)
-        run: mvn --batch-mode -Dskip.unit.tests=true verify
+        run: |
+          echo "${{ secrets.KCBQ_TEST_KEYFILE }}" > /tmp/creds.json
+          mvn --batch-mode -Dskip.unit.tests=true verify
         env:
+          # Necessary for client builder integration tests that run with
+          # default application credentials
+          GOOGLE_APPLICATION_CREDENTIALS: /tmp/creds.json
+          KCBQ_TEST_KEY_SOURCE: JSON
           KCBQ_TEST_KEYFILE:    ${{ secrets.KCBQ_TEST_KEYFILE }}
-          KCBQ_TEST_KEY_SOURCE: ${{ secrets.KCBQ_TEST_KEY_SOURCE }}
           KCBQ_TEST_PROJECT:    ${{ secrets.KCBQ_TEST_PROJECT }}
           KCBQ_TEST_DATASET:    ${{ secrets.KCBQ_TEST_DATASET }}
           KCBQ_TEST_BUCKET:     ${{ secrets.KCBQ_TEST_BUCKET }}