Pytester.runpytest_subprocess only adds the first plugin from pytester.plugins

[Faboor]

When adding multiple plugins to pytester.plugins only the first one is added as a -p <plugin> to the command line invocation in pytester.runpytest_subprocess().

Minimal example:

# Content of test_minimal.py:

def test_pytester_minimal(pytester):
    pytester.plugins.extend(["no:plug_1", "no:plug_2"])
    pytester.runpytest_subprocess()

$ pytest --version
pytest 8.3.5

$ pytest -p pytester -rP test_minimal.py
...
__________ test_pytester_minimal __________
---------- Captured stdout call ----------
running: /Users/Faboor/Projects/pytester/venv/bin/python3.12 -mpytest -p no:plug_1 --basetemp=/private/var/folders/q0/x7bql_wd1f9gw5y8rb15tg240000gq/T/pytest-of-Faboor/pytest-5/test_pytester_minimal0/runpytest-0
...

Notice that only -p no:plug_1 is added.

[nicoddemus]

Fixed by #13522.