Make the integration test optional (#67)

.github/workflows/test.yml

@@ -10,14 +10,22 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v3
+      - uses: actions/setup-node@v3
+        with:
+          node-version: 16
+          cache: yarn
       - run: yarn install --frozen-lockfile
       - run: yarn run yarn-deduplicate --fail --strategy fewer
       - run: yarn run build
       - run: yarn run prettier --check
       - run: yarn run xo
+      # Optional integration test of the action using a dedicated GitHub App.
       - id: generate_token
+        if: ${{ vars.TEST_GITHUB_APP_ID != '' }}
         uses: ./
         with:
+          # The only required permission is `Repository permissions > Metadata: Read-only`.
           app_id: ${{ vars.TEST_GITHUB_APP_ID }}
           private_key: ${{ secrets.TEST_GITHUB_APP_PRIVATE_KEY }}
       - run: node --eval "assert('${{ steps.generate_token.outputs.token }}'.length > 0);"
+        if: ${{ steps.generate_token.outcome != 'skipped' }}