[Ready] Remove Python 3.6 from tests in GH Actions

[chusloj]

This PR removes Python 3.6 from the GH action's test suite. Addresses #2582.

cc @MattHJensen

[jdebacker]

@chusloj Thanks for taking care of this! Do you want to try to see if we can get code coverage working now (uncommenting the upload report lines)? Also, we might want to add pycodestyle testing back, which was dropped with the GH Action, I think.

[codecov]

Codecov Report

Merging #2584 (46dcd32) into master (d3c7037) will decrease coverage by 1.45%.
The diff coverage is 97.14%.

@@            Coverage Diff             @@
##           master    #2584      +/-   ##
==========================================
- Coverage   99.92%   98.46%   -1.46%     
==========================================
  Files          13       14       +1     
  Lines        2591     2611      +20     
==========================================
- Hits         2589     2571      -18     
- Misses          2       40      +38     

Flag	Coverage Δ
unittests	98.46% <97.14%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
taxcalc/data.py	99.24% <66.66%> (-0.76%)	⬇️
taxcalc/__init__.py	100.00% <100.00%> (ø)
taxcalc/decorators.py	100.00% <100.00%> (ø)
taxcalc/parameters.py	99.31% <100.00%> (-0.02%)	⬇️
taxcalc/utils.py	97.79% <0.00%> (-2.21%)	⬇️
ppp.py	0.00% <0.00%> (ø)

[jdebacker]

Code coverage is back! Thanks @chusloj!

[chusloj]

@jdebacker Code coverage is back, but pycodestyle tests interfere with the test suite profiling, so that has been left out.

@MattHJensen In the environment file, fsspec has to be temporarily pinned to <=0.8.7 due to an issue in reading files from the web which is causing Paramtools to fail to read JSON files from URLs (see here for a similar issue with the Pangeo project). cc @hdoupe

[MattHJensen]

@chusloj could you help me understand that 1.45% reported reduction in code coverage?

[chusloj]

@MattHJensen Looks like coverage now is compared to coverage from the last PR merged before codecov was shut off, which looks to be #2512. Regarding this patch, codecov says that this ValueError message in the Data class is not covered:

Tax-Calculator/taxcalc/data.py

Line 104 in 46dcd32

raise ValueError("Data has more records than weights.")