fix(material-experimental/mdc-snack-bar): increase the specificity of

styles targeting the action buttons.

Currently the order of the button theme vs the snackbar theme matters,
this will make the snackbar theme always take precedence

Author: mmalerba

src/material-experimental/mdc-snack-bar/_snack-bar-theme.scss

@@ -36,7 +36,7 @@
   mdc-snackbar.$dismiss-ink-color: $orig-dismiss-ink-color;
 
   // The extra level of nesting here is to increase the specificity.
-  .mat-mdc-simple-snack-bar .mat-mdc-snack-bar-actions .mdc-snackbar__action {
+  .mat-mdc-simple-snack-bar .mat-mdc-snack-bar-actions .mdc-snackbar__action.mdc-snackbar__action {
     $is-dark-theme: map.get($config, is-dark);
     $accent: map.get($config, accent);
     color: if($is-dark-theme, inherit, theming.get-color-from-palette($accent, text));