Disable the 'reviewers-recommender' job for community MRs

What does this MR do and why?

We noticed that the "Suggested reviewers" message would still show up in the following cases:

• MR from a core team member, e.g. !65883 (comment 969342358)
• Community contribution for which a team member started a pipeline in the canonical namespace (i.e. usually before merging)

We decided in the past that the message is not useful for Community contribution and mostly create noise, so we disabled it for non-canonical pipelines, but this MR also disables the job if the MR has the Community contribution entirely so that we handle the two above cases.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.