add workflow_dispatch to ci.yml

[braingram]

Checklist

• [ ] added entry in CHANGES.rst (either in Bug Fixes or Changes to API)
• [ ] updated relevant tests
• [ ] updated relevant documentation
• [ ] updated relevant milestone(s)
• [ ] added relevant label(s)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

:loudspeaker: Thoughts on this report? Let us know!.

[braingram]

The CI is red because the MIRI apcorr reference files on CRDS were updated to include a CHANNEL parameter which does not match the schema.