[clang] [clang-scan-deps] Enable test P1689.cppm on Windows (PR #145857)

[Naveen Seth Hanig via cfe-commits]

naveen-seth wrote:

I also checked the other tests in `test/ClangScanDeps`. This is currently the only test where Windows is disabled only because of the path seperator difference.

https://github.com/llvm/llvm-project/pull/145857