refactor: improve error message styling for reset password form (#6791)

#### What type of PR is this?

/area core
/kind improvement
/milestone 2.20.x

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

优化重置密码表单的错误提示样式。

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

```release-note
None
```

application/src/main/resources/templates/gateway_modules/form_fragments.html

@@ -248,7 +248,9 @@
     th:action="@{/password-reset/{resetToken}(resetToken=${resetToken})}"
     method="post"
 >
-    <p style="color: red" role="alert" th:if="${error}" th:text="${error}"></p>
+    <div class="alert alert-error" role="alert" th:if="${error}">
+        <strong th:text="${error}"></strong>
+    </div>
     <div class="form-item">
         <label for="password" th:text="#{form.passwordResetLink.password.label}">Password</label>
         <th:block