Fix _extract_template_fields mypy error

[choo121600]

This PR resolves an issue where the mypy-dev pre-commit hook fails during the CI process.

The Problem

When running in CI, the build failed with the following mypy error:

scripts/ci/pre_commit/validate_operators_init.py:63: error: List comprehension
has incompatible type List[str | bytes | int | float | complex | EllipsisType |
None]; expected List[str]  [misc]

Solution

# Before
return [elt.value for elt in class_item.value.elts if isinstance(elt, ast.Constant)]

# After
return [str(elt.value) for elt in class_item.value.elts if isinstance(elt, ast.Constant)]

---

^ Add meaningful description above
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[github-actions]

Backport successfully created: v3-0-test

Status	Branch	Result
✅	v3-0-test