Make Package.verify() raise exception when it have to compute unknown hash type

[sir-sigurd]

TODO

• Unit tests
• Changelog entry (skip if change is not significant to end users, e.g. docs only)

[codecov]

Codecov Report

Merging #3401 (ebb62f8) into master (590439d) will increase coverage by 0.06%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #3401      +/-   ##
==========================================
+ Coverage   36.09%   36.16%   +0.06%     
==========================================
  Files         680      680              
  Lines       29707    29735      +28     
  Branches     4390     4390              
==========================================
+ Hits        10724    10753      +29     
+ Misses      17830    17829       -1     
  Partials     1153     1153              

Flag	Coverage Δ
api-python	91.29% <100.00%> (+0.05%)	⬆️
catalog	10.06% <ø> (ø)
lambda	86.01% <ø> (ø)

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Impacted Files	Coverage Δ
api/python/quilt3/packages.py	93.40% <100.00%> (+0.16%)	⬆️
api/python/tests/integration/test_packages.py	100.00% <100.00%> (ø)

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feedback is addressed