cargo_wrapper: Force log file to be written in utf-8

We can hit https://gitlab.freedesktop.org/HuQian/gstreamer/-/jobs/71717584
otherwise, weirdly it never happened here.

Part-of: <!2114>

cargo_wrapper.py

@@ -76,7 +76,7 @@ if __name__ == "__main__":
     opts = PARSER.parse_args()
     logdir = opts.root_dir / 'meson-logs'
     logfile_path = logdir / f'{opts.src_dir.name}-cargo-wrapper.log'
-    logfile = open(logfile_path, mode='w', buffering=1)
+    logfile = open(logfile_path, mode="w", buffering=1, encoding='utf-8')
 
     print(opts, file=logfile)
     cargo_target_dir = opts.build_dir / 'target'