[easy] fix deprecation warnings for indexing using a sequence

[ttung]

xarray prefers to be indexed with a tuple of selectors rather than a sequence. Update the API to generate tuples and use them instead.

Test plan: Saw fewer deprecation warnings in the test console.

[codecov-io]

Codecov Report

Merging #1690 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1690      +/-   ##
==========================================
+ Coverage   89.85%   89.85%   +<.01%     
==========================================
  Files         239      239              
  Lines        8966     8967       +1     
==========================================
+ Hits         8056     8057       +1     
  Misses        910      910

Impacted Files	Coverage Δ
starfish/core/morphology/binary_mask/expand.py	89.47% <100%> (+0.58%)	⬆️
...tarfish/core/morphology/binary_mask/binary_mask.py	95.08% <100%> (ø)	⬆️

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