Limit about to <200 chars in the infra issue template (#63839)

.github/ISSUE_TEMPLATE/infrastructure.md

 ---
 name: I want to file a bug or feature request about Flutter's CI infrastructure
-about: As a Flutter contributor, you have run into problems with the build/test/release
-  infrastructure, including the build and performance dashboards
-  (http://flutter-dashboard.appspot.com), devicelab, LUCI (https://ci.chromium.org/p/flutter) etc.
-  Or you have new ideas around those systems.
+about: As a contributor, you want to file an issue about the build/test/release
+  infra, e.g. dashboards (http://flutter-dashboard.appspot.com), devicelab,
+  LUCI (https://ci.chromium.org/p/flutter) etc.
 title: ''
 labels: 'team: infra'
 assignees: ''