build(java): use yoshi-approver token for auto-approve (#772)

Author: chingor13

synthtool/gcp/templates/java_library/.github/workflows/auto-release.yaml

@@ -7,7 +7,7 @@ jobs:
     steps:
     - uses: actions/github-script@v3.0.0
       with:
-        github-token: {{ '${{secrets.GITHUB_TOKEN}}' }}
+        github-token: {{ '${{secrets.YOSHI_APPROVER_TOKEN}}' }}
         debug: true
         script: |
           // only approve PRs from release-please[bot]
@@ -66,4 +66,4 @@ jobs:
             repo: context.repo.repo,
             issue_number: context.payload.pull_request.number,
             labels: ['kokoro:force-run', 'automerge']
-          });
+          });