only copy BTI headshape file if present

[sappelhoff]

PR Description

• closes Problems with conversion of BTI datasets #1155

Merge checklist

Maintainer, please confirm the following before merging.
If applicable:

• All comments are resolved
• This is not your own PR
• All CIs are happy
• PR title starts with [MRG]
• whats_new.rst is updated
• New contributors have been added to CITATION.cff
• PR description includes phrase "closes <#issue-number>"

[sappelhoff]

@nugenta please try this fix and tell me whether it solves your mne-bids specific problem. The MNE-Python will hopefully be solved in MNE-Python directly.

You can install this branch like this:

pip uninstall mne_bids
pip install git+https://github.com/sappelhoff/mne-bids.git@bti

Afterwards, uninstall mne-bids again, and re-install it as you had it before.

[codecov]

Codecov Report

Merging #1158 (48c08f7) into main (fd61827) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1158      +/-   ##
==========================================
- Coverage   97.62%   97.62%   -0.01%     
==========================================
  Files          40       40              
  Lines        8644     8640       -4     
==========================================
- Hits         8439     8435       -4     
  Misses        205      205              

Files Changed	Coverage Δ
mne_bids/copyfiles.py	97.71% <100.00%> (-0.02%)	⬇️
mne_bids/inspect.py	98.77% <100.00%> (-0.03%)	⬇️