fix: add CPyWeakref_GetRef to headers

Author: BobTheBuidler

mypyc/lib-rt/CPy.h

@@ -928,6 +928,7 @@ PyObject *CPySingledispatch_RegisterFunction(PyObject *singledispatch_func, PyOb
 
 PyObject *CPy_GetAIter(PyObject *obj);
 PyObject *CPy_GetANext(PyObject *aiter);
+PyObject *CPyWeakref_GetRef(PyObject *ref);
 void CPy_SetTypeAliasTypeComputeFunction(PyObject *alias, PyObject *compute_value);
 void CPyTrace_LogEvent(const char *location, const char *line, const char *op, const char *details);