ci: Run go mod tidy check on submodules

Today, we do not enforce a clean `go mod tidy` on submodules. This
allows for drift and can eventually lead to `golangci-lint` failures,
along with the obvious disadvantage of not having an up-to-date
`go.mod`.

Enforce clean `go mod tidy` on all `go.mod` by using our make target
rather than the direct root-level command.

.github/workflows/reusable-check-go-mod.yml

@@ -26,7 +26,8 @@ jobs:
     - uses: actions/setup-go@fac708d6674e30b6ba41289acaab6d4b75aa0753 # v4.0.1
       with:
         go-version-file: 'go.mod'
-    - run: go mod tidy
+    # Run on all go.mod (include submodules).
+    - run: make go-mod-tidy
     - run: |
         if [[ -n $(git status -s) ]]; then
           echo "Git directory has changes"