Fix warnings

```
▹  tests.cpyext.test_modsupport
        ↳  TestCase.runClass.<locals>.ThisTestCase.setUpClass  /Users/lewurm/work/graalpython/mxbuild/jdk17/com.oracle.graal.python.test/bin/tests/cpyext/parseargs_es.c:14:24: warning: pas
sing 'const char *' to parameter of type 'void *' discards qualifiers [-Wincompatible-pointer-types-discards-qualifiers]
            PyMem_Free(out);
                       ^~~
/Users/lewurm/work/graalpython/graalpython/include/pymem.h:59:35: note: passing argument to parameter 'ptr' here                                                                            PyAPI_FUNC(void) PyMem_Free(void *ptr);
                                  ^
1 warning generated.
/Users/lewurm/work/graalpython/mxbuild/jdk17/com.oracle.graal.python.test/bin/tests/cpyext/parseargs_et.c:14:24: warning: passing 'const char *' to parameter of type 'void *' discards qual
ifiers [-Wincompatible-pointer-types-discards-qualifiers]
            PyMem_Free(out);
                       ^~~
/Users/lewurm/work/graalpython/graalpython/include/pymem.h:59:35: note: passing argument to parameter 'ptr' here
PyAPI_FUNC(void) PyMem_Free(void *ptr);
                                  ^
1 warning generated.
```

Author: lewurm

graalpython/com.oracle.graal.python.test/src/tests/cpyext/test_modsupport.py

@@ -537,7 +537,7 @@ def compile_module(self, name):
         ),
         code='''
         static PyObject * wrap_PyArg_ParseTuple(PyObject* argTuple) {
-            const char * out;
+            char * out;
             Py_INCREF(argTuple);
             if (PyArg_ParseTuple(argTuple, "es", "UTF-8", &out) == 0) {
                 return NULL;
@@ -562,7 +562,7 @@ def compile_module(self, name):
         ),
         code='''
         static PyObject * wrap_PyArg_ParseTuple(PyObject* argTuple) {
-            const char * out;
+            char * out;
             Py_INCREF(argTuple);
             if (PyArg_ParseTuple(argTuple, "es", "UTF-8", &out) == 0) {
                 return NULL;