Remove py and pytest-forked test dependencies (#15501)

We don't use either of these in our own code at all. Neither of them
should be needed in 2023.

py used to be a dependency of pytest but no longer is. It was added to
test-requirements.txt 6 years ago in order to pin a specific version to
fix an issue where some tests were failing:
5168c25
and
ad6dd4e.

pytest-forked used to be a dependency of pytest-xdist, but no longer is.
It was added to test-requirements.txt` 4 years ago in order to pin a
specific version to fix builds on macOS:
e006b94.

test-requirements.txt

@@ -11,9 +11,7 @@ psutil>=4.0
 # pytest 6.2.3 does not support Python 3.10
 pytest>=6.2.4
 pytest-xdist>=1.34.0
-pytest-forked>=1.3.0,<2.0.0
 pytest-cov>=2.10.0
-py>=1.5.2
 ruff==0.0.272  # must match version in .pre-commit-config.yaml
 setuptools>=65.5.1
 six