[ONPREM-4] Update runner component CODEOWNERS

[Stuart133]

Checklist

=========

• [*] I have performed a self-review of my own code
• [*] This is not a security issue (which should be reported here: https://circleci.com/security/)
• [*] I have read Contribution Guidelines.

Internal Checklist

• [*] I am requesting a review from my own team as well as the owning team

Changes

=======

Update CODEOWNERS with new runner team

[JulesFaucherre]

Hey @Stuart133 , I don't know if you saw it but apparently there are some errors on the file, the message is the following:

Unknown owner on line 4: make sure the team @CircleCI-Public/on-prem exists, is publicly visible, and has write access to the repository
/api/runner @CircleCI-Public/on-prem

Same for line 5

[Stuart133]

I have opened an IT ticket to get the on-prem team added with write access to this repo which should fix that error

[JulesFaucherre]

Alright, approving it, feel free to merge it once the ticket is addressed then!