[analyzer] Properly close analyzer WATCHLISTS entry

I didn't adjust this when removing nnbd_migration in https://dart-review.googlesource.com/c/sdk/+/340160.

Change-Id: I21829c3052be1671a2407f219a332a7a62197ce5
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/340361
Reviewed-by: Alexander Thomas <athom@google.com>
Auto-Submit: Parker Lougheed <parlough@gmail.com>
Commit-Queue: Alexander Thomas <athom@google.com>
Reviewed-by: Samuel Rawlins <srawlins@google.com>

WATCHLISTS

@@ -19,7 +19,7 @@
         '^pkg/analyzer_plugin|'
         '^pkg/analyzer_utilities|'
         '^pkg/linter|'
-        '^pkg/meta|'
+        '^pkg/meta'
       )
     },
     'build': {