Merge branch 'ide-firefox-scroll-fix' into 'master'

Fixed IDE sidebar not being scrollable in FireFox

Closes #45314

See merge request gitlab-org/gitlab-ce!18350

app/assets/stylesheets/pages/repo.scss

@@ -429,6 +429,7 @@
   .projects-sidebar {
     display: flex;
     flex-direction: column;
+    height: 100%;
 
     .context-header {
       width: auto;
@@ -438,8 +439,8 @@
 
   .multi-file-commit-panel-inner {
     display: flex;
-    flex: 1;
     flex-direction: column;
+    height: 100%;
   }
 
   .multi-file-commit-panel-inner-scroll {