Merge branch 'mattermost-5.25.3' into 'master'

Update Mattermost to 5.25.3

See merge request gitlab-org/omnibus-gitlab!4499

changelogs/unreleased/mattermost-5-25-1.yml

 ---
-title: Update Mattermost to 5.25.2
+title: Update Mattermost to 5.25.3
 merge_request:
 author:
 type: other

config/software/mattermost.rb

@@ -17,10 +17,10 @@
 #
 name 'mattermost'
-default_version '5.25.2'
+default_version '5.25.3'
 source url: "https://releases.mattermost.com/#{version}/mattermost-team-#{version}-linux-amd64.tar.gz",
-       md5: 'c3153f95500391ba7bec69d79923bc10'
+       md5: 'e786c7a090da4d68a952caf6d4d8509a'
 relative_path 'mattermost'