Pin text I/O to UTF-8 and fail CI on locale-dependent reads/writes (#3296)

Co-authored-by: ShuQingDollarVoyager <57471784+ShuQingDollarVoyager@users.noreply.github.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

tests/test_types.py

@@ -495,9 +495,9 @@ def test_bare_import_mcp_binds_the_types_submodule():
     # A regression hangs forever, so the bound only has to beat never (matches the suite's
     # other subprocess.run calls).
     result = subprocess.run(
-        [sys.executable, "-c", "import mcp; print(mcp.types.Tool.__name__)"],
+        [sys.executable, "-X", "utf8", "-c", "import mcp; print(mcp.types.Tool.__name__)"],
         capture_output=True,
-        text=True,
+        encoding="utf-8",
         check=False,
         timeout=20,
     )