Set ensure_ascii=False in JSON dump within apply_chat_template

[junrae6454]

What does this PR do?

• This PR modifies the apply_chat_template function to improve handling of non-ASCII characters in JSON output by setting ensure_ascii to False. This change ensures that characters such as "안녕?" and emojis are correctly rendered in their original form rather than as escaped sequences.
• Modified the ImmutableSandboxedEnvironment in apply_chat_template to set ensure_ascii=False in jinja_env.policies['json.dumps_kwargs'].

Before

try:
    import jinja2
    from jinja2.exceptions import TemplateError
    from jinja2.sandbox import ImmutableSandboxedEnvironment
except ImportError:
    raise ImportError("apply_chat_template requires jinja2 to be installed.")

def raise_exception(message):
    raise TemplateError(message)

jinja_env = ImmutableSandboxedEnvironment(trim_blocks=True, lstrip_blocks=True)
jinja_env.globals["raise_exception"] = raise_exception
template = jinja_env.from_string("{{tools|tojson}}")
template.render(tools={"안녕?":"🤗"})

>>> '{"\\uc548\\ub155?": "\\ud83e\\udd17"}'

After

try:
    import jinja2
    from jinja2.exceptions import TemplateError
    from jinja2.sandbox import ImmutableSandboxedEnvironment
except ImportError:
    raise ImportError("apply_chat_template requires jinja2 to be installed.")

def raise_exception(message):
    raise TemplateError(message)

jinja_env = ImmutableSandboxedEnvironment(trim_blocks=True, lstrip_blocks=True)
jinja_env.globals["raise_exception"] = raise_exception
jinja_env.policies['json.dumps_kwargs']['ensure_ascii'] = False
template = jinja_env.from_string("{{tools|tojson}}")
template.render(tools={"안녕?":"🤗"})

>>> '{"안녕?": "🤗"}'

Fixes # (issue)

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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  here are tips on formatting docstrings.
• Did you write any new necessary tests?

Who can review?

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
members/contributors who may be interested in your PR.

• I think @Rocketknight1 would be a good choice for review.

[CISC]

Hey, very cool that there are more than just me using tojson, but it's a duplicate of #31041 :)

[Rocketknight1]

Hi @junrae6454, thank you for this PR! As mentioned, this is a duplicate of the earlier PR #31041, so I'm going to close it, but we appreciate the contribution, and feel free to add any comments or suggestions on that PR!