MNT: Test on Python 3.10

[effigies]

Should be advertising that we support 3.9. Checking that we support 3.10 while we're at it.

Next minor release should drop support for 3.6.

[codecov]

Codecov Report

Merging #3438 (9ae5c67) into master (96c50f2) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #3438   +/-   ##
=======================================
  Coverage   65.21%   65.21%           
=======================================
  Files         307      307           
  Lines       40487    40507   +20     
  Branches     5353     5353           
=======================================
+ Hits        26403    26417   +14     
- Misses      13008    13014    +6     
  Partials     1076     1076           

Flag	Coverage Δ
unittests	64.94% <100.00%> (ø)

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

Impacted Files	Coverage Δ
nipype/info.py	92.18% <ø> (ø)
nipype/sphinxext/apidoc/__init__.py	28.20% <100.00%> (ø)
nipype/sphinxext/apidoc/docstring.py	16.00% <100.00%> (ø)
nipype/pipeline/plugins/sgegraph.py	11.36% <0.00%> (-0.14%)	⬇️
nipype/pipeline/plugins/slurmgraph.py	10.98% <0.00%> (-0.13%)	⬇️
nipype/algorithms/misc.py	45.13% <0.00%> (-0.11%)	⬇️
nipype/pipeline/plugins/sge.py	18.10% <0.00%> (-0.08%)	⬇️
nipype/interfaces/cmtk/cmtk.py	17.89% <0.00%> (-0.08%)	⬇️
nipype/interfaces/freesurfer/base.py	76.61% <0.00%> (ø)
nipype/interfaces/minc/minc.py	85.20% <0.00%> (+0.01%)	⬆️
... and 8 more

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