For Bazel builds, mark some of the low-level tests that are dependent

on timing as flaky.

This will run them up to 3 times (in the default configuration) and only
consider the test failed if it fails each time.

PiperOrigin-RevId: 530348477
Change-Id: Ib77bd8a166828b82a1b49ee5ef2e8321752e51d0

absl/synchronization/BUILD.bazel

@@ -238,6 +238,7 @@ cc_test(
     size = "large",
     srcs = ["mutex_test.cc"],
     copts = ABSL_TEST_COPTS,
+    flaky = 1,
     linkopts = ABSL_DEFAULT_LINKOPTS,
     shard_count = 25,
     deps = [
@@ -300,6 +301,7 @@ cc_test(
     size = "small",
     srcs = ["notification_test.cc"],
     copts = ABSL_TEST_COPTS,
+    flaky = 1,
     linkopts = ABSL_DEFAULT_LINKOPTS,
     tags = ["no_test_lexan"],
     deps = [