Fix the following build issue [1] that was introduced by [2].

  src/plugins/python_plugins.c: In function 'python_env_init':
  src/plugins/python_plugins.c:98:91: error: 'Py_XDECREF' undeclared
    (first use in this function); did you mean 'Py_DecRef'?

[1]
https://github.com/profanity-im/profanity/issues/2043

[2]
https://github.com/profanity-im/profanity/commit/c0da36c4

--- a/src/plugins/python_plugins.c      2025-07-31 15:18:09
+++ b/src/plugins/python_plugins.c      2025-07-31 15:18:17
@@ -86,10 +86,16 @@ python_get_version_number(void)
     return version_number;
 }
 
+static void
+_unref_module(PyObject* module)
+{
+    Py_XDECREF(module);
+}
+
 void
 python_env_init(void)
 {
-    loaded_modules = g_hash_table_new_full(g_str_hash, g_str_equal, free, (GDestroyNotify)Py_XDECREF);
+    loaded_modules = g_hash_table_new_full(g_str_hash, g_str_equal, free, (GDestroyNotify)_unref_module);
 
     python_init_prof();