Fix a compiler warning: use unsigned int type instead of enum PyUnicode_Kind to

compare two Unicode kinds

Python/formatter_unicode.c

@@ -556,7 +556,7 @@ fill_number(_PyUnicodeWriter *writer, const NumberFieldWidths *spec,
 {
     /* Used to keep track of digits, decimal, and remainder. */
     Py_ssize_t d_pos = d_start;
-    const enum PyUnicode_Kind kind = writer->kind;
+    const unsigned int kind = writer->kind;
     const void *data = writer->data;
     Py_ssize_t r;