Merge branch 'ph/212455/fixedTreeBorderOnFirefox' into 'master'

Fixes the tree border on FireFox

Closes #212455

See merge request gitlab-org/gitlab!28311

app/assets/stylesheets/pages/tree.scss

@@ -120,6 +120,7 @@
       &:hover:not(.tree-truncated-warning) {
         td {
           background-color: $blue-50;
+          background-clip: padding-box;
           border-top: 1px solid $blue-200;
           border-bottom: 1px solid $blue-200;
           cursor: pointer;