Replaces runtime.GOOS with 'win32' in the test archive filename within TestDownloadCopilot. This ensures the test uses the expected archive name for Windows.
copilot
Signed-off-by: Babak K. Shandiz <babakks@github.com> Co-authored-by: Kynan Ware <bagtoad@github.com> Co-authored-by: Devraj Mehta <devm33@github.com>