POST should be PUT in the API labels specs

What does this MR do?

When looking through the specs I saw there were two specs using a POST request within the PUT specs.

Does this MR meet the acceptance criteria?

• [-] Changelog entry added, if necessary
• [-] Documentation created/updated
• [-] Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides