docs: Use current color for autorefs external link icon

Author: pawamoy

docs/css/mkdocstrings.css

@@ -18,10 +18,10 @@ a.autorefs-external::after {
 
   height: 1em;
   width: 1em;
-  background-color: var(--md-typeset-a-color);
+  background-color: currentColor;
 }
 
 a.external:hover::after,
 a.autorefs-external:hover::after {
   background-color: var(--md-accent-fg-color);
-}
+}