`local_runtime_repo` writes absolute path of Xcode on macOS

# 🐞 bug report

(Sorry for all the annoying macOS specific bugs!)

### Affected Rule

The issue is caused by the rule: `local_runtime_repo`

### Is this a regression?

Yes(?)

### Description

Starting with this change: https://github.com/bazel-contrib/rules_python/pull/2760/files#diff-33a51eb016b4b2a4b53d940f07c5388bd572ef61689051bc6f266ea7e5533c72R99

If running on macOS, `/usr/bin/python3` is a system shim that will run a Python runtime located within Xcode. The path of Xcode will then show up in `base_executable`:

```
❯ /usr/bin/python3 python/private/get_local_runtime_info.py
{"major": 3, "minor": 9, "micro": 6, "include": "/Library/Python/3.9/include", "implementation_name": "cpython", "base_executable": "/Applications/Xcode-26.0.0-Beta.app/Contents/Developer/usr/bin/python3", "LDLIBRARY": "Python3.framework/Versions/3.9/Python3", "LIBDIR": "/Applications/Xcode.app/Contents/Developer/Library/Frameworks/Python3.framework/Versions/3.9/lib", "INSTSONAME": "Python3.framework/Versions/3.9/Python3", "PY3LIBRARY": "", "SHLIB_SUFFIX": ".so"}
```

This path then ends up in the run script for i.e. `py_binary`:

```
76: PYTHON_BINARY = '/Applications/Xcode-26.0.0-Beta.app/Contents/Developer/usr/bin/python3'
```

## 🔬 Minimal Reproduction

1. macOS
2. `local_runtime_repo` setup with `interpreter_path = "/usr/bin/python3"`
3. build a `py_binary` target and observe the resulting run script
4. Change/move your Xcode version or path and rebuild. The `py_binary` path will be unchanged.

python/private/get_local_runtime_info.py と local_runtime_repo ルールから始め、次に interpreter_path="/usr/bin/python3" と py_binary ターゲットを使って macOS のケースを再現します。base_executable が生成された実行スクリプトにどのように到達するかを追跡します。Xcode を変更または移動した後に再ビルドしても、そのスクリプトに古い Xcode パスが埋め込まれたままにならなければ完了です。

索引モデルが issue の本文から書いたものです。