gha-ci: instruct bazelisk to use previous bazel version

Bazel 7 is the latest release, but it cannot build Protobuf 25.1:

        ERROR: no such package '@@com_google_protobuf//': The repository
	'@@com_google_protobuf' could not be resolved: Repository
	'@@com_google_protobuf' is not defined

Change-Id: I5a43ac6ea157056b6e40f1ccc2621b7808613b55
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/552075
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Lasse Folger <lassefolger@google.com>

.github/workflows/test.yml

@@ -27,4 +27,7 @@ jobs:
           ~/.cache/bazel
         key: ${{ runner.os }}-${{ hashFiles('integration_test.go') }}
     - name: Test
+      env:
+        # Protobuf 25 does not yet support Bazel 7
+        USE_BAZEL_VERSION: latest-1
       run: go test -run='^TestIntegration$' -v -timeout=60m -count=1 -failfast "$@"