mattermost update to 10.6.1-bb.3

Package Merge Request

Package Changes

https://repo1.dso.mil/big-bang/product/packages/mattermost/-/blob/10.6.1-bb.3/CHANGELOG.md

Package MR

big-bang/product/packages/mattermost!303 (merged)

For Issue

Closes big-bang/product/packages/mattermost#205 (closed)

Upgrade Notices

N/A