Bump Jinja2 upper-bound from 2.12.0 to 4.0.0

[ashwin153]

• Closes Support for Jinja2 3.x #16591.

[boring-cyborg]

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[uranusjr]

What is the <3.1.0 upper bound for?

[ashwin153]

Was just preserving behavior. Will remove.

[potiuk]

Can you please rebase @ashwin153 ?

[boring-cyborg]

Awesome work, congrats on your first merged pull request!