Fix vendored Font Awesome not rendered correctly

Refs. #3544

Author: mshibuya

vendor/assets/stylesheets/rails_admin/font-awesome.scss

@@ -14,7 +14,9 @@
   font-display: block;
   src: asset-url("rails_admin/fa-solid-900.woff2") format("woff2"), asset-url("rails_admin/fa-solid-900.ttf") format("truetype"); }
 
-.fa {
+.fa,
+.fas,
+.fa-solid {
   font-family: var(--fa-style-family, "Font Awesome 6 Free");
   font-weight: var(--fa-style, 900); }