fix create user bug (#2317)

src/user/UserForm.tsx

@@ -409,7 +409,11 @@ export const UserForm = ({
       <ActionGroup>
         <Button
           data-testid={!user?.id ? "create-user" : "save-user"}
-          isDisabled={!user?.id && !watchUsernameInput}
+          isDisabled={
+            !user?.id &&
+            !watchUsernameInput &&
+            !realm?.registrationEmailAsUsername
+          }
           variant="primary"
           type="submit"
         >

src/user/UsersTabs.tsx

@@ -152,9 +152,7 @@ const UsersTabs = () => {
       <ImpersonateConfirm />
       <DeleteConfirm />
       <ViewHeader
-        titleKey={
-          userForm.getValues().username || user?.username || t("createUser")
-        }
+        titleKey={user?.id ? user.username! : t("createUser")}
         divider={!id}
         dropdownItems={[
           <DropdownItem