ref: require choices for ChoiceField to be a Sequence

[asottile-sentry]

when these are unordered collections it causes api-diff to flap.

fixed the one error that was outstanding:

src/sentry/replays/validators.py:56: error: Argument "choices" to "MultipleChoiceField" has incompatible type "Set[str]"; expected "Sequence[Any]"  [arg-type]

[codecov]

Codecov Report

Merging #53707 (3f82f76) into master (6ce9614) will decrease coverage by 0.01%.
Report is 6 commits behind head on master.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #53707      +/-   ##
==========================================
- Coverage   79.50%   79.50%   -0.01%     
==========================================
  Files        4951     4951              
  Lines      209200   209200              
  Branches    35637    35637              
==========================================
- Hits       166328   166324       -4     
- Misses      37784    37789       +5     
+ Partials     5088     5087       -1     

Files Changed	Coverage Δ
src/sentry/replays/validators.py	100.00% <100.00%> (ø)

... and 4 files with indirect coverage changes