update or downgrade go modules to match debian versions

- use go 1.22 (as available also in bookworm-backports)
- do not install go mods in docker

.github/workflows/ci.yml

@@ -82,11 +82,6 @@ jobs:
           sudo mkdir -p /srv ; sudo chown runner /srv
           COVERAGE_DIR=${{ runner.temp }} make all
 
-      - name: "Install Go 1.22 for merging coverage"
-        uses: actions/setup-go@v3
-        with:
-          go-version: 1.22
-
       - name: Merge code coverage
         run: |
           go install github.com/wadey/gocovmerge@latest