Update Mattermost to 6.3.4

Package Merge Request

Package Changes

Update MM to 6.3.4

Package MR

https://repo1.dso.mil/platform-one/big-bang/apps/collaboration-tools/mattermost/-/merge_requests/85

For Issue

Closes https://repo1.dso.mil/platform-one/big-bang/apps/collaboration-tools/mattermost/-/issues/44 (sort of)

changed milestone to %1.28.0

added mattermost statusreview labels

assigned to @micah.nagel

marked this merge request as ready

requested review from @BrandenCobb

changed title from Update Mattermost to 5.3.4 to Update Mattermost to 6.3.4

changed the description

approved this merge request

enabled an automatic merge when the pipeline for efd24b8a succeeds

merged

mentioned in commit 6e389eb4

picked the changes into the branch release-1.28.x with commit bd1fcc80

mentioned in commit bd1fcc80