fix get OS on some of the windows computers

[BoYanZh]

At least on my laptop, $(OS) returns Windows instead of Windows_NT. So I try to fix it.

[codecov-commenter]

Codecov Report

Merging #16007 (f26a356) into main (b4d1059) will increase coverage by 0.03%.
The diff coverage is 75.00%.

@@            Coverage Diff             @@
##             main   #16007      +/-   ##
==========================================
+ Coverage   44.02%   44.06%   +0.03%     
==========================================
  Files         682      682              
  Lines       82407    82412       +5     
==========================================
+ Hits        36282    36311      +29     
+ Misses      40218    40202      -16     
+ Partials     5907     5899       -8     

Impacted Files	Coverage Δ
modules/auth/sso/reverseproxy.go	8.51% <0.00%> (ø)
services/repository/generate.go	0.00% <0.00%> (ø)
modules/web/middleware/cookie.go	64.65% <66.66%> (+7.75%)	⬆️
modules/markup/markdown/goldmark.go	58.84% <70.00%> (+0.62%)	⬆️
modules/auth/sso/basic.go	44.64% <100.00%> (ø)
modules/auth/sso/sso.go	36.66% <100.00%> (ø)
modules/markup/sanitizer.go	88.88% <100.00%> (ø)
modules/setting/indexer.go	91.42% <100.00%> (ø)
modules/setting/queue.go	67.92% <100.00%> (ø)
routers/repo/pull.go	31.15% <100.00%> (+0.07%)	⬆️
... and 8 more

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