Merge branch 'cb-omnibus-mattermost-version-docs' into 'master'

Update Omnibus Mattermost versions

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/145224



Merged-by: Evan Read <eread@gitlab.com>
Approved-by: Evan Read <eread@gitlab.com>
Co-authored-by: Clemens Beck <cbeck@gitlab.com>

doc/integration/mattermost/index.md

@@ -359,6 +359,7 @@ Below is a list of Mattermost version changes for GitLab 14.0 and later:
 
 | GitLab version | Mattermost version | Notes                                                                                    |
 | :------------- | :----------------- | ---------------------------------------------------------------------------------------- |
+| 16.9           | 9.4                |                                                                                          |
 | 16.7           | 9.3                |                                                                                          |
 | 16.6           | 9.1                |                                                                                          |
 | 16.5           | 9.0                |                                                                                          |