Fix missing underline on focus states for anchor tags

app/assets/stylesheets/bootstrap_migration.scss

@@ -89,6 +89,11 @@ a {
   color: $gl-link-color;
 }
 
+a:not(.btn):focus,
+a:not(.btn):active {
+  text-decoration: underline;
+}
+
 hr {
   overflow: hidden;
 }

app/assets/stylesheets/framework/contextual_sidebar.scss

@@ -193,6 +193,7 @@
       &:focus {
         background: $link-active-background;
         color: $gl-text-color;
+        text-decoration: none;
       }
     }