Fix CLI compilation on Windows.

[mattmoyer]

It turns out that syscall.Stdin is of type int on Linux and macOS, but not on Windows (it's syscall.Handle). This should now be portable and do all the required type casting on every platform.

This is a recently introduced regression (in #687), so it has never been released. We are also adjusting the CI pipeline to include a Windows CLI compilation in the PR pipeline (which allowed this regression to slip into main unnoticed).

Release note:

NONE

[codecov]

Codecov Report

Merging #746 (8e8af51) into main (d5759c9) will increase coverage by 0.00%.
The diff coverage is 50.00%.

@@           Coverage Diff           @@
##             main     #746   +/-   ##
=======================================
  Coverage   79.85%   79.86%           
=======================================
  Files         124      124           
  Lines        8346     8347    +1     
=======================================
+ Hits         6665     6666    +1     
  Misses       1463     1463           
  Partials      218      218           

Impacted Files	Coverage Δ
pkg/oidcclient/login.go	89.75% <50.00%> (+0.02%)	⬆️

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