[core] fix test_import_in_subprocess in windows

[sampan-s-nayak]

Description

test_import_in_subprocess was failing on windows as return subprocess.run(["python", "-c", "import pip_install_test"]) would use system python instead of the virtualenv's python

warning highlighted in python subprocess docs:

Warning For maximum reliability, use a fully qualified path for the executable. To search for an unqualified name on PATH, use shutil.which(). On all platforms, passing sys.executable is the recommended way to launch the current Python interpreter again, and use the -m command-line format to launch an installed module.

https://docs.python.org/3/library/subprocess.html

test passed (but looks like some other unrelated tests failed):
https://buildkite.com/organizations/ray-project/pipelines/premerge/builds/57162/jobs/019b9c44-0ec0-457b-8b8a-dac06d5ea818/log#13851-14985
https://buildkite.com/ray-project/premerge/builds/57254#019ba0e5-9bf8-4157-b997-2a2e4e01358b/L11484

Related issues

Additional information

[gemini-code-assist]

Code Review

This pull request fixes test_import_in_subprocess on Windows by replacing the hardcoded "python" executable with sys.executable in the subprocess.run call. This is a good improvement for cross-platform compatibility, as it ensures the correct Python interpreter from the runtime environment is used. I have one minor suggestion to improve code clarity.