fix: Welcome mailer stopped for non signup oauth (#27053)

## Description
> This PR fixes the error introduced in
https://github.com/appsmithorg/appsmith/pull/25854 which lead to sending
of welcome mails even for non signup - oauth type requests.

#### PR fixes following issue(s)
Fixes #27054 
> if no issue exists, please create an issue and ask the maintainers
about this first
>
>
#### Media
> A video or a GIF is preferred. when using Loom, don’t embed because it
looks like it’s a GIF. instead, just link to the video
>
>
#### Type of change

- Bug fix
>
>
>
## Testing
>
#### How Has This Been Tested?
> Please describe the tests that you ran to verify your changes. Also
list any relevant details for your test configuration.
> Delete anything that is not relevant
- [ ] Manual
- [ ] JUnit
- [ ] Jest
- [ ] Cypress
>
>
#### Test Plan
> Add Testsmith test cases links that relate to this PR
>
>
#### Issues raised during DP testing
> Link issues raised during DP testing for better visiblity and tracking
(copy link from comments dropped on this PR)
>
>
>
## Checklist:
#### Dev activity
- [ ] My code follows the style guidelines of this project
- [ ] I have performed a self-review of my own code
- [ ] I have commented my code, particularly in hard-to-understand areas
- [ ] I have made corresponding changes to the documentation
- [ ] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] New and existing unit tests pass locally with my changes
- [ ] PR is being merged under a feature flag


#### QA activity:
- [ ] [Speedbreak
features](https://github.com/appsmithorg/TestSmith/wiki/Guidelines-for-test-plans#speedbreakers-)
have been covered
- [ ] Test plan covers all impacted features and [areas of
interest](https://github.com/appsmithorg/TestSmith/wiki/Guidelines-for-test-plans#areas-of-interest-)
- [ ] Test plan has been peer reviewed by project stakeholders and other
QA members
- [ ] Manually tested functionality on DP
- [ ] We had an implementation alignment call with stakeholders post QA
Round 2
- [ ] Cypress test cases have been added and approved by SDET/manual QA
- [ ] Added `Test Plan Approved` label after Cypress tests were reviewed
- [ ] Added `Test Plan Approved` label after JUnit tests were reviewed

app/server/appsmith-server/src/main/java/com/appsmith/server/authentication/handlers/ce/AuthenticationSuccessHandlerCE.java

@@ -313,9 +313,7 @@ public class AuthenticationSuccessHandlerCE implements ServerAuthenticationSucce
                                     .then(handleOAuth2Redirect(webFilterExchange, null, finalIsFromSignup));
                         });
             } else {
-                redirectionMono = userService
-                        .sendWelcomeEmail(user, originHeader)
-                        .then(handleOAuth2Redirect(webFilterExchange, null, isFromSignup));
+                redirectionMono = handleOAuth2Redirect(webFilterExchange, null, isFromSignup);
             }
         } else {
             // form type signup/login handler