ci: run apt update before installing packages

We've seen some issues with 'coverage' job that failed
to install 'go' package. This is possibly caused by
outdated repository information in the CI image. Running
`apt update` could fix it.

.github/workflows/tests.yml

@@ -161,6 +161,7 @@ jobs:
     steps:
       - name: Install dependencies
         run: |
+          sudo apt update
           sudo apt install -yqq golang
           go install github.com/boumenot/[email protected]