Avoid labeling all PRs as 'text-input' (flutter#157805)

After flutter#157650 all PRs are being labeled as text-input by the PR labeler. I think the config is missing an `all` based on the [negation example](https://github.com/actions/labeler/blob/main/README.md#basic-examples)

Author: jmagman

.github/labeler.yml

@@ -39,9 +39,9 @@
 
 'a: text input':
   - changed-files:
-    - any-glob-to-any-file:
-      - '**/text/*'
+    - all-globs-to-any-file:
       - '**/*text*'
+      - '!**/*context*'
 
 'd: api docs':
   - changed-files: