[Bug]: py_test venv building doesn't work with slash in the name

[keith]

What happened?

If you have a target like this:

py_test(
    name = "pytest_test/nested",
    srcs = [
        "foo_test.py",
        ":__test__",
    ],
    env_inherit = ["FOO"],
    imports = ["../.."],
    main = ":__test__.py",
    package_collisions = "warning",
    deps = [
        ":__test__",
        "@pypi_ftfy//:pkg",
        "@pypi_neptune//:pkg",
        "@pypi_pytest//:pkg",
    ],
)

Running this test works with rules_python and fails with rules_py with:

Error:   × Unable to run command:
  ├─▶ Unable to get full source dir path
  ╰─▶ No such file or directory (os error 2)

Version

Development (host) and target OS/architectures: Ubuntu 22.04

Output of bazel --version: 7.4.0

Version of the Aspect rules, or other relevant rules from your
WORKSPACE or MODULE.bazel file:

Language(s) and/or frameworks involved:

How to reproduce

Run the test modified on this branch: #484

Any other information?

No response

[keith]

adding some logging I bet the issue is that this path join:

"/home/ubuntu/.cache/bazel/_bazel_ubuntu/cbd66eedddd4d083f5e4d752aed24a45/sandbox/linux-sandbox/19/execroot/aspect_rules_py/bazel-out/k8-fastbuild/bin/examples/pytest/pytest_test/nested.runfiles/.pytest_test/nested.venv/lib/python3.9/site-packages" ::: "../../../../pypi_exceptiongroup/site-packages"

the second path is off by 1 ../ because of the target adding another level of nesting