chore(deps): update actions/cache action to v4 (#576)

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Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.github/workflows/buildtest.yaml

@@ -26,7 +26,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@3df4ab11eba7bda6032a0b82a6bb43b11571feac # v4
-    - uses: actions/cache@v3
+    - uses: actions/cache@v4
       with:
         path: |
           ~/go/pkg/mod