py/parse: Use m_renew_maybe to ensure that memory is shrunk in-place.

The chunks of memory that the parser allocates contain parse nodes and
are pointed to from many places, so these chunks cannot be relocated
by the memory manager.  This patch makes it so that when a chunk is
shrunk to fit, it is not relocated.

py/parse.c

@@ -166,8 +166,8 @@ STATIC void *parser_alloc(parser_t *parser, size_t num_bytes) {
             sizeof(mp_parse_chunk_t) + chunk->alloc + num_bytes, false);
         if (new_data == NULL) {
             // could not grow existing memory; shrink it to fit previous
-            (void)m_renew(byte, chunk, sizeof(mp_parse_chunk_t) + chunk->alloc,
-                sizeof(mp_parse_chunk_t) + chunk->union_.used);
+            (void)m_renew_maybe(byte, chunk, sizeof(mp_parse_chunk_t) + chunk->alloc,
+                sizeof(mp_parse_chunk_t) + chunk->union_.used, false);
             chunk->alloc = chunk->union_.used;
             chunk->union_.next = parser->tree.chunk;
             parser->tree.chunk = chunk;