Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/testing.yml

@@ -43,7 +43,7 @@ jobs:
           go-version: ${{ matrix.go }}
 
       - name: Check out code into the Go module directory
-        uses: actions/checkout@692973e3d937129bcbf40652eb9f2f61becf3332 # v4.1.7
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
         with:
           persist-credentials: false
           fetch-depth: 0