chore(deps): update actions/setup-go action to v6 (#628)

Author: gardener-ci-robot

.github/actions/prepare-release/action.yaml

@@ -3,7 +3,7 @@ name: Prepare Release
 runs:
   using: composite
   steps:
-    - uses: actions/setup-go@v5
+    - uses: actions/setup-go@v6
       with:
         go-version: '1.25'
     - name: make-generate

.github/workflows/build.yaml

@@ -115,7 +115,7 @@ jobs:
   verify:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/setup-go@v5
+      - uses: actions/setup-go@v6
         with:
           go-version: '1.25'
       - uses: gardener/cc-utils/.github/actions/trusted-checkout@master

.github/workflows/vendor_gardener.yaml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v4
-    - uses: actions/setup-go@v5
+    - uses: actions/setup-go@v6
       with:
         go-version-file: go.mod