Update Mac_mokey microbenchmarks with issue to the bringup: true in ci config for easier discovery (#164694)

Update the comment in .ci.yaml with the issue link for easier discovery.
Related issue: #156506
Related discussion: flutter/flutter#162000

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

Author: harri35

.ci.yaml

@@ -4691,7 +4691,7 @@ targets:
   - name: Mac_mokey microbenchmarks
     recipe: devicelab/devicelab_drone
     presubmit: false
-    bringup: true # Flaky: codefu
+    bringup: true # TODO(codefu): https://github.com/flutter/flutter/issues/156506
     timeout: 60
     properties:
       tags: >