v0.18.0 breaks and rearranges lines, hence fails, -> LibUp failing on GrowthExperiments

[micgro42]

See T387519 stylelint breaks and rearranges lines, hence fails, -> LibUp failing

Below is a copy of that task's description for conveninence:

Steps to replicate the issue (include links if applicable):

• Check out the GrowthExperiments repository
• Run npm add --save-dev stylelint-config-wikimedia@0.18.0 to update the stylelint config
• Run npm t to run all the tests

What happens?:

modules/ext.growthExperiments.Homepage.styles/SuggestedEditsModule.less
   99:25  ✖  Needless disable for "declaration-no-important"  --report-needless-disables
  102:3   ✖  Unexpected !important                            declaration-no-important
  341:26  ✖  Needless disable for "declaration-no-important"  --report-needless-disables
  342:11  ✖  Unexpected !important                            declaration-no-important

✖ 4 problems (4 errors, 0 warnings)

What should have happened instead?:
Stylelint should have finished without errors

Other information:

The first location in question:

097 .mw-mf-page-center__mask.suggested-edits {
098 	// Set value to be higher than Minerva's overlay content (@z-indexOverlay: 3).
099 	z-index: 4 !important; // stylelint-disable-line declaration-no-important
100 }
101
102 .drawer.suggested-edits-taskexplanation-drawer {
103 	h4 {

This seems to be among the issues that cause #libup to fail for GrowthExperiments.