Pin GitHub Action digests

Author: lberrymage

.github/workflows/buf.yaml

@@ -18,8 +18,8 @@ jobs:
   buf:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
-      - uses: bufbuild/buf-action@v1
+      - uses: actions/checkout@93cb6efe18208431cddfb8368fd83d5badbf9bfd # v5.0.1
+      - uses: bufbuild/buf-action@fd21066df7214747548607aaa45548ba2b9bc1ff # v1.4.0
         with:
           format: false
           token: ${{ secrets.BUF_TOKEN }}