Update capi_version for mypyc tests to 3.8

[cdce8p]

This PR updates the capi_version used for mypyc tests to 3.8 (mypy / mypyc requires >=3.9). Test data updates done with --update-data. For Python 3.8+ mypyc uses _PyObject_Vectorcall instead of PyObject_CallFunctionObjArgs and PyObject_Call where ever possible.

Will remove the now unnecessary use_vectorcall check in a followup.

mypy/mypyc/common.py

Lines 103 to 105 in aa0b6f0

	def use_vectorcall(capi_version: tuple[int, int]) -> bool:
	# We can use vectorcalls to make calls on Python 3.8+ (PEP 590).
	return capi_version >= (3, 8)

[cdce8p]

PyObject_Vectorcall is available unconditionally from pythoncapi_compat.h. Included the underscore removal here so I wouldn't have to do another big PR just for that.

mypy/mypyc/lib-rt/pythoncapi_compat.h

Lines 602 to 610 in aa0b6f0

	// gh-105922 added PyObject_Vectorcall() to Python 3.9.0a4
	#if PY_VERSION_HEX < 0x030900A4
	static inline PyObject*
	PyObject_Vectorcall(PyObject *callable, PyObject *const *args,
	size_t nargsf, PyObject *kwnames)
	{
	#if PY_VERSION_HEX >= 0x030800B1 && !defined(PYPY_VERSION)
	// bpo-36974 added _PyObject_Vectorcall() to Python 3.8.0b1
	return _PyObject_Vectorcall(callable, args, nargsf, kwnames);