Runfiles API fails when code and output_user_root are on different Windows drives.

# 🐞 bug report

### Affected Rule

`python.runfiles`

### Is this a regression?

I'm not sure, I've never seen it but I rarely use windows.

### Description

It seems if a repo is checked out to a different drive than the bazel output_base then the runfiles API breaks.

https://github.com/UebelAndre/rules_pytest/actions/runs/10495890608/job/29075336459

## 🔬 Minimal Reproduction

On https://github.com/UebelAndre/rules_pytest/tree/abb7f0e6598cb267a704e189237a14b5d777532d run:
```
bazel test //python/pytest/private/tests/version_test
```

## 🔥 Exception or Error

```
__________________________________________ test_versions __________________________________________
(19:07:33) INFO: Found 28 targets and 20 test targets...

def test_versions() -> None:
"""Test that the version.bzl and MOUDLE.bazel versions are synced."""
runfiles = Runfiles.Create()
if not runfiles:
raise EnvironmentError("Failed to locate runfiles.")

> version_bzl = rlocation(runfiles, "rules_pytest/version.bzl")

D:\a\rules_pytest\rules_pytest\python\pytest\private\tests\version_test\version_test.py:35:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
D:\a\rules_pytest\rules_pytest\python\pytest\private\tests\version_test\version_test.py:20: in rlocation
runfile = runfiles.Rlocation(rlocationpath)
..\rules_python\python\runfiles\runfiles.py:175: in Rlocation
source_repo = self.CurrentRepository(frame=2)
..\rules_python\python\runfiles\runfiles.py:248: in CurrentRepository
caller_runfiles_path = os.path.relpath(caller_path, self._python_runfiles_root)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

path = 'D:\\a\\rules_pytest\\rules_pytest\\python\\pytest\\private\\tests\\version_test\\version_test.py'
start = 'C:\\Users\\RUNNER~1\\AppData\\Local\\Temp\\Bazel.runfiles_ycjtfwtt\\runfiles'

> ???
E ValueError: path is on mount 'D:', start on mount 'C:'

:766: ValueError
```

## 🌍 Your Environment

**Operating System:**

  

windows

  

**Output of `bazel version`:**

  

Bazelisk version: 1.20.0

Build label: 7.3.1

Build target: @@//src/main/java/com/google/devtools/build/lib/bazel:BazelServer

Build time: Mon Aug 19 16:41:27 2024 (1724085687)

Build timestamp: 1724085687

Build timestamp as int: 1724085687

  

**Rules_python version:**

  

0.34.0

  

**Anything else relevant?**

python/runfiles/runfiles.py、特に Rlocation と CurrentRepository から始め、次に、リポジトリと出力ルートを異なるドライブに置いた状態で、Windows 上で bazel test //python/pytest/private/tests/version_test を実行して失敗を再現します。version_test.py の traceback に、失敗しているパス操作が示されています。再現がドライブ間の ValueError なしに完了し、その動作が適切なテストでカバーされれば完了です。

索引モデルが issue の本文から書いたものです。