Fix mis-wording

What does this MR do and why?

Describe in detail what your merge request does and why.

I think the docs are supposed to say "when" rather than unless. alternatively it could mean "We do not run the minimal RSpec & Jest jobs for fork pipelines unless the pipeline:run-all-rspec label is set on the MR. The goal is to reduce the CI/CD minutes consumed by fork pipelines."

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

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.