copy-code: don't hide outline on :focus. Closes #12118.

Author: cscheid

src/resources/formats/html/_quarto-rules-copy-code.scss

@@ -9,10 +9,6 @@
   z-index: 3;
 }
 
-.code-copy-button:focus {
-  outline: none;
-}
-
 .code-copy-button-tooltip {
   font-size: 0.75em;
 }