Merge branch 'ph/focusCopyCodeButton' into 'master'

Allow copy code button to be focusable

See merge request gitlab-org/gitlab!76889

app/assets/stylesheets/framework/buttons.scss

@@ -460,7 +460,8 @@ copy-code {
   top: 7px;
   right: $input-horizontal-padding;
 
-  .markdown-code-block:hover & {
+  .markdown-code-block:hover &,
+  &:focus-within {
     @include gl-opacity-10;
   }
 }