set meshio<5.2 for sphinx builds

[CagtayFabry]

Changes

• set meshio<5.2 in the sphinx environment to avoid import error
  https://github.com/BAMWelDX/weldx/runs/4570280776?check_suite_focus=true

Related Issues

Closes #672

I am not sure why this only pops up in the sphinx build, do we have a test using meshio? @vhirtham

[codecov]

Codecov Report

Merging #673 (6568313) into master (463f949) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #673   +/-   ##
=======================================
  Coverage   96.16%   96.16%           
=======================================
  Files          91       91           
  Lines        5941     5941           
=======================================
  Hits         5713     5713           
  Misses        228      228           

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[github-actions]

Unit Test Results

       1 files  ±0         1 suites  ±0   2m 8s ⏱️ +35s
1 949 tests ±0  1 949 ✔️ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit 6568313. ± Comparison against base commit 463f949.

[vhirtham]

I am not sure why this only pops up in the sphinx build, do we have a test using meshio? @vhirtham

Not that I am aware of

[marscher]

I have encountered several of these circular import errors during loading Sphinx conf.py. That's why there is this workaround function to load modules like xarray and pandas. I cannot make anything of that strange behaviour as you noticed it only happens in Sphinx builds. So its probably related to the "changed" import behaviour there.