[MRG] Ensure raw.info['bads'] is a list

[hoechenberger]

PR Description

In some cases we created info['bads'] as an ndarray, leading to unexpected behavior. MNE-Python docs say that it's expected to be a list.

Merge checklist

Maintainer, please confirm the following before merging:

• All comments resolved
• This is not your own PR
• All CIs are happy
• PR title starts with [MRG]
• whats_new.rst is updated
• PR description includes phrase "closes <#issue-number>"
• Commit history does not contain any merge commits

[codecov-commenter]

Codecov Report

Merging #501 into master will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #501      +/-   ##
==========================================
+ Coverage   92.79%   92.82%   +0.03%     
==========================================
  Files          14       14              
  Lines        1970     1980      +10     
==========================================
+ Hits         1828     1838      +10     
  Misses        142      142              

Impacted Files	Coverage Δ
mne_bids/read.py	95.95% <100.00%> (+0.13%)	⬆️
mne_bids/write.py	96.75% <100.00%> (+<0.01%)	⬆️

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[sappelhoff]

Thanks @hoechenberger