fix: Add override OS and linux default to platform

[thomasrockhu-codecov]

fixes #471

Allows for users to set an OS to override detection. Also selects linux as the default

[codecov]

Codecov Report

Merging #485 (6feb914) into master (17debce) will decrease coverage by 0.54%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #485      +/-   ##
==========================================
- Coverage   96.46%   95.91%   -0.55%     
==========================================
  Files           3        4       +1     
  Lines         113      147      +34     
  Branches       34       40       +6     
==========================================
+ Hits          109      141      +32     
- Misses          4        6       +2     

Flag	Coverage Δ
demo	85.71% <ø> (ø)
macos-latest	95.91% <100.00%> (-0.55%)	⬇️
script	96.99% <100.00%> (-0.99%)	⬇️
ubuntu-latest	95.91% <100.00%> (-0.55%)	⬇️
windows-latest	95.91% <100.00%> (-0.55%)	⬇️

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Impacted Files	Coverage Δ
src/buildExec.ts	99.00% <100.00%> (+1.02%)	⬆️
src/helpers.ts	90.90% <100.00%> (ø)

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