MDL-79099 theme_boost: amend drawer zIndex for use in user tours.

Changed introduced in da2f2c9c modified various zIndex attributes for
the page drawers. This has a side-effect of breaking the user tour of
the course page for the course index.

theme/boost/scss/moodle/drawer.scss

@@ -224,7 +224,8 @@ $right-drawer-width: 320px;
 @include media-breakpoint-up(lg) {
     .drawer {
         // Make sure that in large screens the drawer goes under the drop down menus.
-        z-index: $zindex-dropdown - 1;
+        z-index: inherit;
+
         // Workaround to display the skip link elements from the blocks drawer infront of the navbar.
         // As the skip link is in a fixed position and z-index for this element is ignored
         // then it is hidden behind the top navbar.

theme/boost/style/moodle.css

@@ -30135,7 +30135,7 @@ body.drawer-ease {
 
 @media (min-width: 992px) {
   .drawer {
-    z-index: 999;
+    z-index: inherit;
   }
   .drawer#theme_boost-drawers-blocks:focus-within {
     z-index: 1031;

theme/classic/style/moodle.css

@@ -30135,7 +30135,7 @@ body.drawer-ease {
 
 @media (min-width: 992px) {
   .drawer {
-    z-index: 999;
+    z-index: inherit;
   }
   .drawer#theme_boost-drawers-blocks:focus-within {
     z-index: 1031;