Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/buf.yaml

@@ -18,7 +18,7 @@ jobs:
   buf:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: bufbuild/buf-action@v1
         with:
           format: false

.github/workflows/licensing.yaml

@@ -13,5 +13,5 @@ jobs:
   license-check:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: fsfe/reuse-action@v5