Enable compiling on Windows

[t0yv0]

Fixes #71

This change enables compiling depending projects, such as Terraform Bridge tests, on Windows.

syscall.Stat_t is not defined on windows.

To reproduce, GOOS=windows go build ./....

[codecov]

Codecov Report

Attention: Patch coverage is 47.05882% with 9 lines in your changes are missing coverage. Please review.

Project coverage is 37.38%. Comparing base (dd332f3) to head (47431d4).
Report is 11 commits behind head on main.

Files	Patch %	Lines
pulumitest/copy.go	28.57%	3 Missing and 2 partials ⚠️
pulumitest/fs_unix.go	60.00%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #72      +/-   ##
==========================================
+ Coverage   37.27%   37.38%   +0.10%     
==========================================
  Files          42       43       +1     
  Lines        2664     2675      +11     
==========================================
+ Hits          993     1000       +7     
- Misses       1565     1568       +3     
- Partials      106      107       +1     

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