Handle API errors when failing to join group

app/soapbox/features/group/components/group-action-button.tsx

@@ -55,6 +55,12 @@ const GroupActionButton = ({ group }: IGroupActionButton) => {
           : intl.formatMessage(messages.joinSuccess),
       );
     },
+    onError(error) {
+      const message = (error.response?.data as any).error;
+      if (message) {
+        toast.error(message);
+      }
+    },
   });
 
   const onLeaveGroup = () =>