test(frontend): add RegistrationRequestModalComponent unit tests

[Roshan3580]

Summary

Adds unit tests for RegistrationRequestModalComponent.

Closes #5467

Changes

• Added registration-request-modal.component.spec.ts
• Added a test to verify the component is created successfully
• Added a test to verify modal data correctly seeds name and email
• Added a test to verify null modal data falls back to empty strings
• Added a test to verify getValues() trims whitespace from affiliation and reason

Testing

Executed:

yarn test --include='**/registration-request-modal.component.spec.ts'
yarn lint

Both completed successfully.

[Yicong-Huang]

@Roshan3580 please use our PR template. Please feel free to reopen once it is ready. Thanks!