fix: correct display of email verification message toast (#6822)

#### What type of PR is this?

/area core
/kind bug
/milestone 2.20.x

#### What this PR does / why we need it:

修复不能正常显示邮箱验证提示的问题。

#### Does this PR introduce a user-facing change?

```release-note
None
```

application/src/main/resources/templates/gateway_fragments/signup.html

@@ -128,7 +128,7 @@
                     const email = document.getElementById("email").value;
 
                     if (!email) {
-                        throw new Error(/*[[#{form.signup.emailCode.send.emptyValidation}]]*/"");
+                        throw new Error(/*[[#{form.emailCode.send.emptyValidation}]]*/"");
                     }
 
                     fetch("/signup/send-email-code", {