Mark watch_removed_file_test as flaky.

sdk/lib/_internal/pub/pub.status

Index: sdk/lib/_internal/pub/pub.status
diff --git a/sdk/lib/_internal/pub/pub.status b/sdk/lib/_internal/pub/pub.status
index 1d1dcd0b33745da3f69ccfa56092bdcfa3c618d3..9dd5a3ce961513918c9b0f66d2787c05ece77574 100644
--- a/sdk/lib/_internal/pub/pub.status
+++ b/sdk/lib/_internal/pub/pub.status
@@ -5,6 +5,9 @@
 test/serve/missing_file_test: Pass, Fail # Issue 12570
 test/oauth2/with_an_expired_credentials_refreshes_and_saves_test: Pass, Fail # Issue 12581
 
+[ $runtime == vm && $system == windows ]
+test/serve/watch_removed_file_test: Pass, Fail # Issue 13026
+
 # Issue 12837 is a networking issue on the pub-mac buildbot.
 [ $runtime == vm && $system == macos ]
 test/hosted/remove_removed_dependency_test: Pass, Fail # Issue 12837