mypy

379d59e1 - Fix multiprocessing warnings when runnign tests on Python 3.12 (#16564)

Fix multiprocessing warnings when runnign tests on Python 3.12 (#16564) I saw a bunch of warnings when running tests in parallel using pytest. When running tests sequentially using `-n0` I didn't see warnings. This only seems to happen on Linux. The warnings were like these, which can be fixed by avoiding the use of fork, and using forkserver instead: ``` mypy/test/teststubgen.py::StubgenPythonSuite::stubgen.test::testNestedClass_inspect /usr/local/lib/python3.12/multiprocessing/popen_fork.py:66: DeprecationWarning: This process (pid=84587) is multi-threaded, use of fork() may lead to deadlocks in the child. self.pid = os.fork() ``` Relevant discussion: https://discuss.python.org/t/concerns-regarding-deprecation-of-fork-with-alive-threads/33555