testcase expect_error(): add missing line from rebase

It was supposed to preserve the color for debugging meson project tests!

Fixes: d51e202

mesonbuild/interpreter/interpreter.py

@@ -1481,6 +1481,7 @@ def __init__(self, msg: str, how: str, subproject: str) -> None:
                 super().__init__(subproject)
                 self.old_stdout = sys.stdout
                 sys.stdout = self.new_stdout = io.StringIO()
+                sys.stdout.colorize_console = getattr(self.old_stdout, 'colorize_console', None)
                 self.msg = msg
                 self.how = how