Add the known issue about the timezone handling for the 3.0 series (#18220)

Author: catto

data/release-notes/3-0/0.yml

@@ -128,6 +128,7 @@ sections:
     - Juypter Notebook rendering in the web UI may fail if the notebook includes non UTF-8 encoded characters.
     - Dependency graph fails to parse `setup.py` Python manifest files, resulting in HTTP 500 errors in logs. This, combined with the duplicated logging issue, results in increased root volume utilization.
     - A race condition can cause dependency graph database migrations to appear to fail.
+    - Instances with a custom timezone that were upgraded from an earlier release of GitHub Enterprise Server may have incorrect timestamps in the web UI.
 
   deprecations:
     - heading: Deprecation of GitHub Enterprise Server 2.19

data/release-notes/3-0/1.yml

@@ -40,3 +40,4 @@ sections:
     - 'Repository [deploy keys](/developers/overview/managing-deploy-keys) are unable to be used with repositories containing LFS objects.'
     - 'Juypter Notebook rendering in the web UI may fail if the notebook includes non UTF-8 encoded characters.'
     - 'Dependency graph fails to parse `yarn.lock` Javascript manifest files, resulting in HTTP 500 errors in logs.'
+    - 'Instances with a custom timezone that were upgraded from an earlier release of GitHub Enterprise Server may have incorrect timestamps in the web UI.'