Refactor code in profiles/emails_controller_spec.rb

What does this MR do?

This change is only a minor refactor to the spec file profiles/emails_controller_spec.rb.

Changes

• Usage of let_it_be instead of let where records are created.
• Moving out the subject of each test to the subject variable for re-use across tests.
• Create record using the create method instead of creating record via Rails association.
• Using the non_existing_record_id method to denote the id of a non existent record instead of simply using the value of 1

Benefit

• Moving out the subject helps to add new tests easily and this is required for an upcoming change.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team