go_test with data doesn't work on Windows?

### What version of rules_go are you using?

v0.22.4

### What version of gazelle are you using?

v0.19.0

### What version of Bazel are you using?

3.1.0

### Does this issue reproduce with the latest releases of all the above?

yes

### What operating system and processor architecture are you using?

Windows x64

### Any other potentially useful information about your toolchain?

### What did you do?

https://github.com/ukai/bazel-go-test

### What did you expect to see?

test pass

### What did you see instead?

test failed as it couldn't find testdata file.
```
--- FAIL: TestLoad (0.00s)
sample_test.go:8: Load open testdata/foo: The system cannot find the path specified.; want nil err
FAIL
```

Start by reproducing the linked bazel-go-test example on Windows, then read sample_test.go and the go_test handling of testdata/foo. Done means the test passes and the testdata file is found on Windows.

Written by the indexing model from the issue text.