Manually set library paths in .github/driver.sh

[Alexendoo]

Fixes https://rust-lang.zulipchat.com/#narrow/stream/257328-clippy/topic/Windows.20CI.20failing

Rustup 1.27.1 no longer adds [SYSROOT]/bin to PATH by default - rust-lang/rustup#3825. This is fine for the packaged binaries since windows loads dlls from the folder the executable is in, but our built one is in a different folder

There's an environment variable to get the old behaviour back, but as it's deprecated and not much code I think returning to setting it manually is fine

changelog: none

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[flip1995]

@bors r+

Thanks, I wanted to try to remove the rustup show active-toolchain command anyway.

[bors]

📌 Commit 821dc87 has been approved by flip1995

It is now in the queue for this repository.

[bors]

⌛ Testing commit 821dc87 with merge 6c8ff3f...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: flip1995
Pushing 6c8ff3f to master...