TEST: Pin pytest < 5.1.3

[effigies]

Summary

Seeing if pinning an old pytest resolves #3046.

Acknowledgment

• (Mandatory) I acknowledge that this contribution will be available under the Apache 2 license.

[codecov]

Codecov Report

Merging #3048 into master will decrease coverage by 2.95%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3048      +/-   ##
==========================================
- Coverage   67.03%   64.07%   -2.96%     
==========================================
  Files         343      342       -1     
  Lines       44077    44030      -47     
  Branches     5551     5551              
==========================================
- Hits        29545    28211    -1334     
- Misses      13775    14669     +894     
- Partials      757     1150     +393

Flag	Coverage Δ
#smoketests	?
#unittests	64.07% <ø> (-0.15%)	⬇️

Impacted Files	Coverage Δ
nipype/info.py	88.73% <ø> (-5.64%)	⬇️
nipype/utils/spm_docs.py	25.92% <0%> (-44.45%)	⬇️
nipype/utils/logger.py	59.7% <0%> (-29.86%)	⬇️
nipype/algorithms/rapidart.py	35% <0%> (-29.42%)	⬇️
nipype/utils/provenance.py	55.73% <0%> (-28.35%)	⬇️
nipype/interfaces/spm/base.py	57.94% <0%> (-27.16%)	⬇️
nipype/interfaces/fsl/model.py	54.89% <0%> (-25.73%)	⬇️
nipype/interfaces/matlab.py	64.64% <0%> (-21.22%)	⬇️
nipype/interfaces/nipy/base.py	80% <0%> (-20%)	⬇️
nipype/workflows/fmri/fsl/estimate.py	47.88% <0%> (-16.91%)	⬇️
... and 45 more

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[effigies]

So this appears to be fixing it, but having another look at it, I think the problem is that we're monkey-patching pathlib.Path, rather than providing a replacement, which means we're infecting other tools.