fix(test): fix hash is not stable on Windows

[cscnk52]

On Windows, the path is separated by "\\", not "/", this PR normalize it to prevent hash not stable.

This test was failed on Windows.

---- tests::test_css_modules stdout ----

thread 'tests::test_css_modules' (27464) panicked at src\lib.rs:27055:7:
assertion failed: `(left == right)`

Diff < left / right > :
- <.Ot1kIW_foo {
+ >.EgL3uq_foo {
   background: red;
 }

[kdy1]

This does not account for UNC