pip library import masked by a local directory leading to failures

# 🐞 bug report
I'm seeing an unexpected testing failure when I import `google-cloud-storage` via pip, where there is also a subfolder called `grpc` local to the `py_library` under test.

It feels like a bug in how `py_library` resolves, certainly running the test with `python -m unittest [module]` works in the self-contained repro linked below.

### Affected Rule
`py_library` seems to be most likely rule.

### Is this a regression?
Uncertain, going back a few versions of rules_python hit the same issue.

### Description
The key parts is as follows:

`utils/BUILD.bazel:`
```
load("@rules_python//python:defs.bzl", "py_library", "py_test")

py_library(
name = "utils",
srcs = ["lib.py"],
visibility = ["//:__subpackages__"],
deps = [
"//utils/grpc",
"@pip//google_cloud_storage",
],
)

py_test(
name = "lib_test",
srcs = ["lib_test.py"],
deps = [":utils"],
)
```
The local `utils/grpc` subfolder just contains another trivial `py_library` that has a function that prints to stdout.

## 🔬 Minimal Reproduction
See https://github.com/paulannetts/bazel_py_issue_apr24

## 🔥 Exception or Error
Truncated error of `bazel test //utils:lib_test` (full error log available which jumps via the various pip dependencies of `google_cloud_storage`)

File "/private/var/tmp/_bazel_paul_lu/44119f469120dfe26bc0215a4f182a9c/sandbox/darwin-sandbox/9/execroot/_main/bazel-out/darwin_x86_64-fastbuild/bin/utils/lib_test.runfiles/rules_python~~pip~pip_39_google_auth/site-packages/google/auth/transport/grpc.py", line 37, in 

class AuthMetadataPlugin(grpc.AuthMetadataPlugin):

AttributeError: module 'grpc' has no attribute 'AuthMetadataPlugin'

## 🌍 Your Environment

**Operating System:**
MacOS Sonoma

**Output of `bazel version`:**

  

Bazelisk version: development

Starting local Bazel server and connecting to it...

Build label: 7.1.1

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

Build time: Thu Mar 21 18:08:59 2024 (1711044539)

Build timestamp: 1711044539

Build timestamp as int: 1711044539

  

**Rules_python version:**

`rules_python 0.31.0`

**Other info:**
Using bzlmod
`gazelle 0.35`
`python 3.9`

リンクされた最小再現から始め、`bazel test //utils:lib_test` を実行します。`google_cloud_storage` 依存関係がどのようにインポートされるかを追跡するため、`utils/BUILD.bazel`、`lib.py`、`lib_test.py`、およびローカルの `utils/grpc` ライブラリを読みます。テストが pip 依存関係の代わりにローカルの `grpc` ディレクトリを解決しなくなり、正常にパスすれば完了です。

索引モデルが issue の本文から書いたものです。