Get rid of deprecations

[jacopotediosi]

Hi, I'm an active contributor to OctoPrint core. I helped ship OctoPrint 2.0.0rc1 and I'm now helping plugins stay compatible with the new and upcoming OctoPrint releases, which is why you're receiving this PR.

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What does this PR do and why is it necessary?

This PR fixes the usage of some deprecated stuffs that were causing warnings in OctoPrint's logs.

In particular:

• Enabled is_api_protected (ref)
• Enabled is_template_autoescaped (ref).

A minor improvement is also applied: use is and is not for type comparisons.

How was it tested? How can it be tested by the reviewer?

I tested the installation on both OctoPrint 2.0.0rc1 and the latest stable release 1.11.7, and everything appears to work correctly.

Any background context you want to provide?

What are the relevant tickets if any?

Screenshots (if appropriate)

Further notes