conformance - use utf-8 in open for Windows support

On Windows it failed with
UnicodeDecodeError: 'charmap' codec can't decode byte 0x9d in position 4590: character maps to <undefined>

Author: Andrej730

conformance/src/main.py

@@ -67,7 +67,7 @@ def f(): pass  # E[final]
             {"final": [3, 4]}
         )
     """
-    with open(test_case, "r") as f:
+    with open(test_case, "r", encoding="utf-8") as f:
         lines = f.readlines()
     output: dict[int, tuple[int, int]] = {}
     groups: dict[str, list[int]] = {}

conformance/src/type_checker.py

@@ -325,7 +325,7 @@ def run_tests(self, test_files: Sequence[str]) -> dict[str, str]:
             if not fi.endswith(".py"):
                 continue
             options.tweak(input=fi)
-            with open(fi, "r") as test_file:
+            with open(fi, "r", encoding="utf-8") as test_file:
                 src = test_file.read()
             try:
                 analysis: pytype_analyze.Analysis = pytype_io.check_py(