Fix dart sass 2.0 division deprecations

The src/rails_admin/styles/base/theming.scss used division calculations
which causes deprecation warnings with dart sass >= 2.

The fontawesome-free version also has the same problem.

Using calc() around the division math fixes the issue in theming.scss
Upgrading fontawesome-free to the latest version fixies their issue

Author: darrenterhune

package.json

@@ -15,7 +15,7 @@
   },
   "dependencies": {
     "@babel/runtime": "^7.16.7",
-    "@fortawesome/fontawesome-free": "^5.15.4",
+    "@fortawesome/fontawesome-free": "^6.1.1",
     "@hotwired/turbo-rails": "^7.1.0",
     "@popperjs/core": "^2.11.0",
     "@rails/ujs": "^6.1.4-1",

src/rails_admin/styles/base/theming.scss

@@ -19,7 +19,7 @@ body.rails_admin {
 
       img {
         position: absolute;
-        top: ((40px - $avatar-size) / 2);
+        top: calc((40px - $avatar-size) / 2);
 
         & + span {
           margin-left: ($avatar-size + 5px);
@@ -33,14 +33,14 @@ body.rails_admin {
     padding: 0;
 
     .dropdown-header {
-      padding: ($grid-gutter-width / 2) ($grid-gutter-width / 2) 3px;
+      padding: calc($grid-gutter-width / 2) calc($grid-gutter-width / 2) 3px;
       font-weight: bold;
       color: $gray-700;
       text-transform: uppercase;
     }
 
     > li > a {
-      padding: ($navbar-padding-y / 2) ($grid-gutter-width / 2);
+      padding: calc($navbar-padding-y / 2) calc($grid-gutter-width / 2);
 
       &.active {
         background-color: map-get($theme-colors, primary);