ci: suggest reviewers based on git blame

.github/workflows/auto-assign-reviewers.yml

@@ -0,0 +1,29 @@
+name: Auto Assign Reviewers
+
+# Use a writable token for suggestion comments, including on fork PRs.
+on:
+  pull_request_target:
+    types: [opened, synchronize]
+
+permissions:
+  contents: read
+  pull-requests: write
+
+jobs:
+  assign-reviewers:
+    runs-on: ubuntu-latest
+
+    steps:
+      # Only check out trusted base code: this job holds a writable token.
+      # The action reads changed lines from the pull request files API.
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          ref: ${{ github.event.pull_request.base.sha }}
+          fetch-depth: 0 # Required for git blame
+          persist-credentials: false
+
+      - uses: cachix/git-blame-auto-reviewer@2d112d9bbd60c4feaf2b55e94a058e0e397ab0e0
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}
+          max-reviewers: 3
+          threshold: 20