Stop modifying behavior of yaml on load (#1826)

* Stop modifying behavior of yaml on load

Only modify a copy of ``SafeLoader`` to ensure that we don't change the behaviour of ``pyyaml`` for everyone.

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

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

* Update util.py

Try to address the CodeQL warning.

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

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

* Non-functional commit to trigger the github worklow checks hoping that the codecov isue is resolved.

---------

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

datamodel_code_generator/util.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import copy
 from pathlib import Path
 from typing import TYPE_CHECKING, Any, Callable, Dict, TypeVar
 
@@ -69,9 +70,13 @@ def load_toml(path: Path) -> Dict[str, Any]:
             return toml.load(path)
 
 
-SafeLoader.yaml_constructors[
-    'tag:yaml.org,2002:timestamp'
-] = SafeLoader.yaml_constructors['tag:yaml.org,2002:str']
+SafeLoaderTemp = copy.deepcopy(SafeLoader)
+SafeLoaderTemp.yaml_constructors = copy.deepcopy(SafeLoader.yaml_constructors)
+SafeLoaderTemp.add_constructor(
+    'tag:yaml.org,2002:timestamp',
+    SafeLoaderTemp.yaml_constructors['tag:yaml.org,2002:str'],
+)
+SafeLoader = SafeLoaderTemp
 
 Model = TypeVar('Model', bound=_BaseModel)