CI error: Spawn of mutable special Generic mine had unresolved joins

[SurFlurer]

Describe the bug

There's something strange happening in CI. It says: Spawn of mutable special Generic mine had unresolved joins. Existing terrain at (99,136,-3) was empty_rock; joins were above: tunnel_ramp. I've never saw this while I was playing.

Attach save file

N/A

Steps to reproduce

See https://github.com/CleverRaven/Cataclysm-DDA/actions/runs/10642218816/job/29504958986?pr=76052

Expected behavior

There shouldn't be errors like this.

Screenshots

No response

Versions and configuration

See the pr. The branch is based on 45f35ecb556eae10b78997257765a40795c2784f.

Additional context

No response