fix: enforce UTF-8 encoding for linter subprocess on Windows

src/graylint/linting.py

@@ -308,12 +308,15 @@ def _check_linter_output(
     existing_path_strs = sorted(str(path) for path in paths if (root / path).exists())
     cmdline_and_paths = cmdline_parts + existing_path_strs
     logger.debug("[%s]$ %s", root, shlex.join(cmdline_and_paths))
+    effective_env = env.copy()
+    if WINDOWS:
+        effective_env["PYTHONIOENCODING"] = "utf-8"
     with Popen(  # nosec
         cmdline_and_paths,
         stdout=PIPE,
         encoding="utf-8",
         cwd=root,
-        env=env,
+        env=effective_env,
     ) as linter_process:
         # condition needed for MyPy (see https://stackoverflow.com/q/57350490/15770)
         if linter_process.stdout is None: