ci: add buf lint workflow

Runs `buf lint` on every pull_request and master push. Uses the official
bufbuild/buf-setup-action with the GITHUB_TOKEN to avoid GitHub API rate
limits during buf installation.

Author: rustatian

.github/workflows/buf-lint.yml

@@ -0,0 +1,23 @@
+name: 'Buf Lint'
+
+on:
+  pull_request:
+  push:
+    branches:
+      - master
+
+jobs:
+  lint:
+    name: 'buf lint'
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up buf
+        uses: bufbuild/buf-setup-action@v1
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Lint protofiles
+        run: buf lint