ci: disable setup-go cache to prevent cache poisoning

The build-test workflow runs on push/PR to protected branches; leaving `actions/setup-go` caching on lets a PR-populated cache be restored into a trusted run. Disable it.

Signed-off-by: Benoit Tigeot <benoit.tigeot@lifen.fr>

.github/workflows/build-test.yml

@@ -28,6 +28,7 @@ jobs:
         with:
           go-version: '${{ env.GOLANG_VERSION }}'
           check-latest: true
+          cache: false
       - name: Test source headers are present
         run: make test-source-headers
       - name: Check if go modules need to be tidied