build(java): auto-approve README regeneration (#254)

This PR was generated using Autosynth. 🌈

Synth log will be available here:
https://source.cloud.google.com/results/invocations/1ec5d14a-c645-43bf-bed4-3d6db3957f76/targets

- [ ] To automatically regenerate this PR, check this box.

Source-Link: googleapis/synthtool@7c53709

.github/workflows/approve-readme.yaml

@@ -0,0 +1,54 @@
+on:
+  pull_request:
+name: auto-merge-readme
+jobs:
+  approve:
+    runs-on: ubuntu-latest
+    if: github.repository_owner == 'googleapis' && github.head_ref == 'autosynth-readme'
+    steps:
+      - uses: actions/github-script@v3.0.0
+        with:
+          github-token: ${{secrets.YOSHI_APPROVER_TOKEN}}
+          script: |
+            // only approve PRs from yoshi-automation
+            if (context.payload.pull_request.user.login !== "yoshi-automation") {
+              return;
+            }
+
+            // only approve PRs like "chore: release <release version>"
+            if (!context.payload.pull_request.title === "chore: regenerate README") {
+              return;
+            }
+
+            // only approve PRs with README.md and synth.metadata changes
+            const files = new Set(
+              (
+                await github.paginate(
+                  github.pulls.listFiles.endpoint({
+                    owner: context.repo.owner,
+                    repo: context.repo.repo,
+                    pull_number: context.payload.pull_request.number,
+                  })
+                )
+              ).map(file => file.filename)
+            );
+            if (files.size != 2 || !files.has("README.md") || !files.has(".github/readme/synth.metadata/synth.metadata")) {
+              return;
+            }
+
+            // approve README regeneration PR
+            await github.pulls.createReview({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              body: 'Rubber stamped PR!',
+              pull_number: context.payload.pull_request.number,
+              event: 'APPROVE'
+            });
+
+            // attach automerge label
+            await github.issues.addLabels({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              issue_number: context.payload.pull_request.number,
+              labels: ['automerge']
+            });

synth.metadata

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-iamcredentials.git",
-        "sha": "e201d834a7ab57d4ad928d49be7d4d7e9a61db95"
+        "sha": "da1659767e6411bf70e2a9927b8cd9207f871f11"
       }
     },
     {
@@ -19,7 +19,7 @@
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "27e0e916cbfdb3d5ff6639b686cc04f78a0b0386"
+        "sha": "7c5370937dd9ba9dcf9cd7d2af880a58b389b4f1"
       }
     }
   ],
@@ -43,6 +43,7 @@
     ".github/readme/synth.py",
     ".github/release-please.yml",
     ".github/trusted-contribution.yml",
+    ".github/workflows/approve-readme.yaml",
     ".github/workflows/auto-release.yaml",
     ".github/workflows/ci.yaml",
     ".github/workflows/formatting.yaml",