Update actions/setup-go action to v6

Author: gardener-ci-robot

.github/workflows/build.yaml

@@ -44,7 +44,7 @@ jobs:
   verify:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/setup-go@v5
+      - uses: actions/setup-go@v6
         with:
           go-version: '1.26'
       - uses: gardener/cc-utils/.github/actions/trusted-checkout@master