grcov Windows CI is broken

This has been happening quite a while now. Examples: #6142, #6329, etc. This is annoying.

```
D:\a\_temp\cdb3edd7-d6b0-4e63-aca4-c520e71a2d0b.sh: line 8: /c/Users/runneradmin/.cargo/bin/grcov: No such file or directory
Error: Process completed with exit code 127.
```

I don't have Windows, so I can't reproduce the issue.

This is probably unrelated to #6033.