fix: typo in code completion prompt

[sdirix]

What it does

fix: typo in code completion prompt

fixes #15379

How to test

1. Reset the code completion prompt if you customized it.
2. Run code completion
3. Check output channel that the fixed prompt was used

Breaking changes

• This PR introduces breaking changes and requires careful review. If yes, the breaking changes section in the changelog has been updated.

Attribution

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[sdirix]

I overlooked that #15380 was already opened. Feel free to close this PR in case the other one gets merged at some point.