Replace snake case in mixins and merge_conflicts variables

app/assets/stylesheets/framework/mixins.scss

@@ -3,13 +3,13 @@
  * Mixins with fixed values
  */
 
-@mixin str-truncated($max_width: 82%) {
+@mixin str-truncated($max-width: 82%) {
   display: inline-block;
   overflow: hidden;
   text-overflow: ellipsis;
   vertical-align: top;
   white-space: nowrap;
-  max-width: $max_width;
+  max-width: $max-width;
 }
 
 /*

changelogs/unreleased/replace-all-snake-case-in-scss-variables.yml

+---
+title: Replace snake case in SCSS variables
+merge_request: 20799
+author: George Tsiolis
+type: other