test(bzlmod): enable testing the MODULE.bazel.lock breakage across platforms

Author: aignas

.bazelci/presubmit.yml

@@ -223,6 +223,12 @@ tasks:
     name: "examples/bzlmod: Ubuntu, minimum Bazel"
     working_directory: examples/bzlmod
     platform: ubuntu2004
+    build_flags:
+      - "--lockfile_mode=update"
+    test_flags:
+      - "--lockfile_mode=update"
+    coverage_flags:
+      - "--lockfile_mode=update"
   integration_test_bzlmod_ubuntu:
     <<: *reusable_build_test_all
     <<: *coverage_targets_example_bzlmod

.gitignore

@@ -52,3 +52,4 @@ user.bazelrc
 # MODULE.bazel.lock is ignored for now as per recommendation from upstream.
 # See https://github.com/bazelbuild/bazel/issues/20369
 MODULE.bazel.lock
+!/examples/bzlmod/MODULE.bazel.lock

examples/bzlmod/.bazelrc

@@ -1,5 +1,9 @@
 common --enable_bzlmod
 
+# Update the lockfile by running:
+# bazel mod deps --lockfile_mode=update
+common --lockfile_mode=error
+
 coverage --java_runtime_version=remotejdk_11
 
 test --test_output=errors --enable_runfiles