Fix test names in corelib/.

Without "_test", they aren't run by the test runner.

Change-Id: I073ea7b8e127120b306036ff9bf5f25066133679
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/198080
Auto-Submit: Bob Nystrom <rnystrom@google.com>
Commit-Queue: Bob Nystrom <rnystrom@google.com>
Commit-Queue: Leaf Petersen <leafp@google.com>
Reviewed-by: Leaf Petersen <leafp@google.com>
diff --git a/tests/corelib/weak_mode/README b/tests/corelib_2/weak_mode/README
similarity index 100%
rename from tests/corelib/weak_mode/README
rename to tests/corelib_2/weak_mode/README
diff --git a/tests/corelib/weak_mode/asyncMap_accepts_null.dart b/tests/corelib_2/weak_mode/asyncMap_accepts_null_test.dart
similarity index 100%
rename from tests/corelib/weak_mode/asyncMap_accepts_null.dart
rename to tests/corelib_2/weak_mode/asyncMap_accepts_null_test.dart
diff --git a/tests/corelib/weak_mode/future_sync_accepts_null.dart b/tests/corelib_2/weak_mode/future_sync_accepts_null_test.dart
similarity index 100%
rename from tests/corelib/weak_mode/future_sync_accepts_null.dart
rename to tests/corelib_2/weak_mode/future_sync_accepts_null_test.dart