[DRE-maint] Bug#956218: Update gitlab to 12.9.x release

[Pirate Praveen]

Package: gitlab
Version: 12.8.8-6
Severity: wishlist

Webpack fails with following error during installation (gitlab from 
salsa master and gitaly from salsa master).

ERROR in 
/var/lib/gitlab/.node_modules/markdown-it/lib/common/entities.js
Module not found: Error: Can't resolve 'entities/maps/entities.json' in 
'/var/lib/gitlab/.node_modules/markdown-it/lib/common'
 @ /var/lib/gitlab/.node_modules/markdown-it/lib/common/entities.js 
6:17-55
 @ /var/lib/gitlab/.node_modules/markdown-it/lib/common/utils.js
 @ /var/lib/gitlab/.node_modules/markdown-it/lib/index.js
 @ /var/lib/gitlab/.node_modules/markdown-it/index.js
 @ /var/lib/gitlab/.node_modules/prosemirror-markdown/dist/index.js
 @ ./behaviors/markdown/serializer.js
 @ ./behaviors/markdown/copy_as_gfm.js
 @ ./behaviors/shortcuts/shortcuts_issuable.js
 @ ./pages/projects/issues/show.js
 @ ./pages/projects/issues/show/index.js
 @ multi ./main ./pages/projects/index.js 
./pages/projects/issues/show/index.js