[mypyc] Revert PyObject_GetOptionalAttrString in module shims

PyObject_GetOptionalAttrString was added in CPython 3.13, but the shim
templates #include only <Python.h> -- they don't see CPy.h or the
pythoncapi_compat.h shim from lib-rt -- so on 3.10/3.11/3.12 CI all
shim builds fail with "implicit declaration of function
'PyObject_GetOptionalAttrString'" under -Werror.

Mypy supports 3.10+, so go back to the portable
PyObject_GetAttrString + PyErr_Clear form. Leaving a comment in both
templates explaining why we can't use the cleaner API here.

Author: VaggelisD

mypyc/lib-rt/module_shim.tmpl

@@ -20,11 +20,11 @@ PyInit_{modname}(void)
     // the per-module real init. Deferring this out of the shared lib's own
     // PyInit keeps separate-mode compiled modules from recursively triggering
     // sibling-package __init__.py mid-bootstrap.
-    PyObject *deps_capsule;
-    if (PyObject_GetOptionalAttrString(tmp, "ensure_deps", &deps_capsule) < 0) {{
-        Py_DECREF(tmp);
-        return NULL;
-    }}
+    // PyObject_GetOptionalAttrString would be cleaner, but it's 3.13+ and the
+    // shim deliberately #includes only <Python.h>, so we can't pull in the
+    // pythoncapi_compat.h shim from lib-rt here. AttributeError + PyErr_Clear
+    // is the portable form.
+    PyObject *deps_capsule = PyObject_GetAttrString(tmp, "ensure_deps");
     if (deps_capsule != NULL) {{
         int (*deps_func)(void) = (int (*)(void))PyCapsule_GetPointer(
             deps_capsule, "{libname}.ensure_deps");
@@ -37,6 +37,8 @@ PyInit_{modname}(void)
             Py_DECREF(tmp);
             return NULL;
         }}
+    }} else {{
+        PyErr_Clear();
     }}
     PyObject *capsule = PyObject_GetAttrString(tmp, "init_{full_modname}");
     Py_DECREF(tmp);

mypyc/lib-rt/module_shim_no_gil_multiphase.tmpl

@@ -19,11 +19,11 @@ static int {modname}_exec(PyObject *module)
     // the per-module real init. Deferring this out of the shared lib's own
     // PyInit keeps separate-mode compiled modules from recursively triggering
     // sibling-package __init__.py mid-bootstrap.
-    PyObject *deps_capsule;
-    if (PyObject_GetOptionalAttrString(tmp, "ensure_deps", &deps_capsule) < 0) {{
-        Py_DECREF(tmp);
-        return -1;
-    }}
+    // PyObject_GetOptionalAttrString would be cleaner, but it's 3.13+ and the
+    // shim deliberately #includes only <Python.h>, so we can't pull in the
+    // pythoncapi_compat.h shim from lib-rt here. AttributeError + PyErr_Clear
+    // is the portable form.
+    PyObject *deps_capsule = PyObject_GetAttrString(tmp, "ensure_deps");
     if (deps_capsule != NULL) {{
         int (*deps_func)(void) = (int (*)(void))PyCapsule_GetPointer(
             deps_capsule, "{libname}.ensure_deps");
@@ -36,6 +36,8 @@ static int {modname}_exec(PyObject *module)
             Py_DECREF(tmp);
             return -1;
         }}
+    }} else {{
+        PyErr_Clear();
     }}
     PyObject *capsule = PyObject_GetAttrString(tmp, "exec_{full_modname}");
     Py_DECREF(tmp);