Do not use errors argument when opening a binary file.

mjtest/test/ast_tests.py

@@ -58,7 +58,7 @@ class ASTPrettyPrintTest(BasicSyntaxTest):
 
     def _pretty_print(self, input_file: str, output_file: str) -> Tuple[int, str, str]:
         out, err, rtcode = self.env.run_mj_command(TestMode.ast, input_file)
-        with open(output_file, "wb", errors="backslashreplace") as f:
+        with open(output_file, "wb") as f:
             f.write(out)
             f.flush()
         return rtcode, decode(out), decode(err)