fix(VListGroup): support regexp in the group prop

fixes #7812

Author: KaelWD

packages/vuetify/src/components/VList/VListGroup.ts

@@ -65,7 +65,7 @@ export default baseMixins.extend<options>().extend({
       default: 'primary',
     },
     disabled: Boolean,
-    group: String,
+    group: [String, RegExp],
     noAction: Boolean,
     prependIcon: String,
     ripple: {