bpo-34589: Make _PyCoreConfig.coerce_c_locale private (GH-9371)

_PyCoreConfig:

* Rename coerce_c_locale to _coerce_c_locale
* Rename coerce_c_locale_warn to _coerce_c_locale_warn

These fields are now private (name prefixed by "_").
diff --git a/Modules/_testcapimodule.c b/Modules/_testcapimodule.c
index add642f..c21a6e3 100644
--- a/Modules/_testcapimodule.c
+++ b/Modules/_testcapimodule.c
@@ -4701,10 +4701,6 @@
              PyLong_FromLong(config->dump_refs));
     SET_ITEM("malloc_stats",
              PyLong_FromLong(config->malloc_stats));
-    SET_ITEM("coerce_c_locale",
-             PyLong_FromLong(config->coerce_c_locale));
-    SET_ITEM("coerce_c_locale_warn",
-             PyLong_FromLong(config->coerce_c_locale_warn));
     SET_ITEM("filesystem_encoding",
              FROM_STRING(config->filesystem_encoding));
     SET_ITEM("filesystem_errors",
@@ -4783,6 +4779,10 @@
              FROM_STRING(config->_check_hash_pycs_mode));
     SET_ITEM("_frozen",
              PyLong_FromLong(config->_frozen));
+    SET_ITEM("_coerce_c_locale",
+             PyLong_FromLong(config->_coerce_c_locale));
+    SET_ITEM("_coerce_c_locale_warn",
+             PyLong_FromLong(config->_coerce_c_locale_warn));
 
     return dict;