Update actions/cache action to v6

Author: renovate[bot]

.github/workflows/testing.yml

@@ -49,7 +49,7 @@ jobs:
           fetch-depth: 0
 
       - name: Cache go module
-        uses: actions/cache@668228422ae6a00e4ad889ee87cd7109ec5666a7 # v5.0.4
+        uses: actions/cache@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6.1.0
         with:
           path: |
             ~/.cache/go-build