fix: use regional terrain for headshop

[0Monet]

Checklist

Required

• I wrote the PR title in conventional commit format.
• I ran the code formatter.
• I linked any relevant issues using github keyword syntax so it can be closed automatically.
• I have committed my changes to new branch that isn't main so it won't cause conflict when updating main branch later.

Purpose of change

Use regional terrain for the mapgen headshop

Describe the solution

Replace non-regional outdoor terrain with pseudo-regional terrain.

Describe alternatives you've considered

none

Additional context

Before:

After: