Building godot docs produces WARNING: Pygments lexer name 'gitignore' is not known

[jynus]

Your Godot version:

This is HEAD of docs at the moment (6b8faf3)

Issue description:

When rebuilding Godot's documentation, I found a WARNING that didn't use to happen beforehand for file tutorials/best_practices/version_control_systems.html

When investigating, it was introduced at pull request #10857 when a snippet of:

.. code-block:: gitignore

Was added. I double checked that I had the latest version of pygments and there is not such a code for syntax-highligting of git. This is not a me-only issue, as official docs can be seen with this code block not being correctly highlighted.

URL to the documentation page:

https://docs.godotengine.org/en/latest/tutorials/best_practices/version_control_systems.html

Suggested fix:

There is, however, a package called pygments-git that -if installed-, could provide the potentially desired highlighting, but with the slightly different name:

.. code-block:: git-ignore

Resulting in this:

Let me know if you prefer the added package to requirements for correct highlighting, or falling back to a more generic "unixconfig" or "ini" supported code block. I would love to get rid of warnings on build (happy to send either pull request). 💙

[jynus]

Personally, I'd prefer not to add the extra dependency- it doesn't look to me like a very popular package, to be honest (it is on pip but not on my distro, for example).