Fix find_exe tests when programs dont exist

[Erotemic]

Fixes #113

[codecov]

Codecov Report

Merging #114 (2808e31) into main (d65d51f) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main      #114   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           28        28           
  Lines         3185      3185           
  Branches       641       641           
=========================================
  Hits          3185      3185           

Impacted Files	Coverage Δ
ubelt/util_platform.py	100.00% <ø> (ø)
ubelt/__init__.py	100.00% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update d65d51f...2808e31. Read the comment docs.