[Net] Fix get_response_body_length for large files.

Parsing was fixed, but not the return value for the exposed getter.

core/io/http_client_tcp.cpp

@@ -534,7 +534,7 @@ Error HTTPClientTCP::poll() {
 	return OK;
 }
 
-int HTTPClientTCP::get_response_body_length() const {
+int64_t HTTPClientTCP::get_response_body_length() const {
 	return body_size;
 }