Default to utf-8 when reading files in :class:.Code (#2703)

* Update code_mobject.py

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: LingrenKong

manim/mobject/text/code_mobject.py

@@ -199,7 +199,7 @@ def __init__(
         self.file_name = file_name
         if self.file_name:
             self._ensure_valid_file()
-            with open(self.file_path) as f:
+            with open(self.file_path, encoding="utf-8") as f:
                 self.code_string = f.read()
         elif code:
             self.code_string = code