Switch to pytest, and bump dependency on Python (3.7) and datalad (0.17)

[mih]

TODO

• [x] The extension or one test is broken with git-annex 10.20220526-gc6b112108 (linux) and 10.20220624 (brew) -- last known-to-work version is 10.20220504 https://github.com/datalad/datalad-ukbiobank/issues/89

[codecov[bot]]

Codecov Report

Merging #87 (7c57492) into main (47037ec) will decrease coverage by 2.50%. The diff coverage is 50.00%.

@@            Coverage Diff             @@
##             main      #87      +/-   ##
==========================================
- Coverage   97.07%   94.57%   -2.51%     
==========================================
  Files           9       10       +1     
  Lines         342      350       +8     
==========================================
- Hits          332      331       -1     
- Misses         10       19       +9     

Impacted Files	Coverage Δ
datalad_ukbiobank/__init__.py	100.00% <ø> (ø)
datalad_ukbiobank/tests/__init__.py	100.00% <ø> (ø)
datalad_ukbiobank/conftest.py	18.18% <18.18%> (ø)
datalad_ukbiobank/tests/test_init.py	100.00% <100.00%> (ø)
datalad_ukbiobank/tests/test_update.py	100.00% <100.00%> (ø)

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