feat: Add Windows-specific env var to default passthroughs (#11126)
### Description
In https://github.com/vercel/turborepo/issues/11114, dotnet on Windows
wasn't working for an unexpected reason. It turned out that there's a
`ProgramFiles(x86)` environment variable that's important to the setup.
I did some digging and this is what I found:
> On 64-bit Windows, 32-bit applications are typically installed in a
separate directory to maintain compatibility and prevent conflicts with
64-bit applications. This directory is designated by ProgramFiles(x86).
This sounds like it fits into being a part of our default passthroughs,
given its system-level nature.
### Testing Instructions
CI