[DRE-maint] Bug#977751: gitlab: node-css-loader 4.x transition

[Pirate Praveen]

Package: gitlab
Version: 13.4.7-2
Severity: important
Control: block 977701 by -1

Updating node-css-loader to 4.x breaks gitlab functionaity.
See upstream ci failure https://gitlab.com/pravi/gitlab/-/jobs/922873794

This needs to be fixed before trying to migrate to node-css-loader 5.x 
which is required for postcss 8 (required by some plugins in unstable).