Fix tests that use xTB on Windows

[shoubhikraj]

The decorator @requires_with_working_xtb_install would previously always return on Windows since the .exe extension is returned by shutil. This PR fixes that bug.

(I didn't update the changelog because this should be covered under making autodE run on windows, I just didn't notice the issue in the previous PR)

---

Checklist

• The changes include an associated explanation of how/why
• Test pass
• Documentation has been updated
• Changelog has been updated

[codecov]

Codecov Report

Merging #250 (c495575) into v1.4.0 (1f42142) will increase coverage by 0.48%.
The diff coverage is 100.00%.

❗ Current head c495575 differs from pull request most recent head f1c21e3. Consider uploading reports for the commit f1c21e3 to get more accurate results

@@            Coverage Diff             @@
##           v1.4.0     #250      +/-   ##
==========================================
+ Coverage   96.86%   97.34%   +0.48%     
==========================================
  Files         195      195              
  Lines       20403    20410       +7     
==========================================
+ Hits        19763    19868     +105     
+ Misses        640      542      -98     

Flag	Coverage Δ
unittests	97.34% <100.00%> (+0.48%)	⬆️

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

Impacted Files	Coverage Δ
tests/test_utils.py	97.37% <100.00%> (+14.55%)	⬆️
tests/testutils.py	94.59% <100.00%> (+0.30%)	⬆️
tests/test_graphs.py	100.00% <0.00%> (+1.06%)	⬆️
tests/test_ts/test_ts_template.py	97.52% <0.00%> (+1.65%)	⬆️
autode/mol_graphs.py	98.34% <0.00%> (+4.29%)	⬆️
autode/utils.py	95.45% <0.00%> (+12.21%)	⬆️

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

[shoubhikraj]

@t-young31 Could you please sync the master branch and the v1.4.0 branch because I am getting merge conflicts (from the doc updates, changelog etc. of v1.3.5 that wasn't present when the 1.4.0 branch was created)

[shoubhikraj]

The codecov test is failing on the upload stage, not sure why.

[shoubhikraj]

@t-young31 This PR is ready for review btw. I don't really know how to increase the diff hit for codecov because I have to see if the xTB is in path to be able to test the wrapper.

[shoubhikraj]

@t-young31 Could you please rerun the pytest-codecov in windows, there is some error in uploading stage.

[t-young31]

Added a tiny suggestion 👍🏼