fix(VSnackbar): don't use !important for box-shadow

fixes #13438

Author: KaelWD

packages/vuetify/src/components/VSnackbar/VSnackbar.sass

@@ -101,7 +101,7 @@
     left: auto
 
   &:not(.v-snack--has-background) &__wrapper
-    box-shadow: none !important
+    box-shadow: none
 
   &--bottom
     top: auto