Do not use PyImport_GetModule() in older PyPy versions that do not have it (GH-4055)

Cython/Utility/ImportExport.c

@@ -58,7 +58,7 @@ bad:
 #if PY_MAJOR_VERSION >= 3
 static PyObject *__Pyx__ImportDottedModule_Lookup(PyObject *name) {
     PyObject *imported_module;
-#if PY_VERSION_HEX < 0x030700A1
+#if PY_VERSION_HEX < 0x030700A1 || (CYTHON_COMPILING_IN_PYPY && PYPY_VERSION_NUM  < 0x07030400)
     PyObject *modules = PyImport_GetModuleDict();
     if (unlikely(!modules))
         return NULL;