Give GitLab doc pages consistent names

The existing end-user doc uses the correct spelling: GitLab.
Let's use the same for the new sysadmins doc :)

refs sysadmin#17733

wiki/src/contribute/working_together/GitLab.mdwn

@@ -437,4 +437,4 @@ Please check these views once in a while and talk to us! :)
 # Operations
 
 See our documentation about [[GitLab for Tails
-sysadmins|contribute/working_together/roles/sysadmins/gitlab]].
+sysadmins|contribute/working_together/roles/sysadmins/GitLab]].

wiki/src/contribute/working_together/roles/sysadmins.mdwn

@@ -239,7 +239,7 @@ Below, importance level is evaluated based on:
   - host Tails issues
   - host most Tails [[Git repositories|contribute/git]]
 * access: public + some data with more restricted access
-* operations documentation: [[contribute/working_together/roles/sysadmins/gitlab]]
+* operations documentation: [[contribute/working_together/roles/sysadmins/GitLab]]
 * end-user documentation: [[contribute/working_together/GitLab]]
 * configuration:
   - immerda hosts our GitLab instance using [this Puppet
@@ -251,7 +251,7 @@ Below, importance level is evaluated based on:
      - configuration: [[!tails_gitlab tails/gitlab-config]]
 * importance: critical (needed to release Tails)
 * Tails system administrators administrate this GitLab instance.
-* See our [[documentation about GitLab for Tails sysadmins|contribute/working_together/roles/sysadmins/gitlab]].
+* See our [[documentation about GitLab for Tails sysadmins|contribute/working_together/roles/sysadmins/GitLab]].
 
 ## Gitolite