Refactor create merge request test suite

What does this MR do?

Move the simplest test to the top and the more complex one to the bottom.

The title of the more complex test case was updated to describe better what it does.

Also, now both it statements are part of the same describe.

Finally, remove duplication of strings by defining variables and re-using them.

What are the relevant issue numbers?

None.

Does this MR meet the acceptance criteria?

• [-] Changelog entry added, if necessary
• [-] Documentation created/updated via this MR
• [-] Documentation reviewed by technical writer or follow-up review issue created
• [-] Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• [-] Conforms to the database guides
• [-] Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• Security reports checked/validated by reviewer