fix(OpenAPI): YAML schema dump

[floxay]

Description

Fixes an issue in the OpenAPI YAML schema dump logic of OpenAPIController where the endpoint for the OpenAPI YAML schema file returns an empty response if a request has been made to the OpenAPI JSON schema previously due to an incorrect variable check.

Closes

Edit from @Alc-Alc: https://discord.com/channels/919193495116337154/919193495690936353/1246024918487793744 explains the need for this

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 98.28%. Comparing base (972ee67) to head (efa4fd1).

Files	Patch %	Lines
litestar/openapi/controller.py	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3537   +/-   ##
=======================================
  Coverage   98.28%   98.28%           
=======================================
  Files         328      328           
  Lines       14848    14848           
  Branches     2358     2358           
=======================================
  Hits        14593    14593           
  Misses        116      116           
  Partials      139      139           

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[Alc-Alc]

does this need a test? if so how to test it? but its a go from me 🙂

[github-actions]

Documentation preview will be available shortly at https://litestar-org.github.io/litestar-docs-preview/3537

[floxay]

does this need a test? if so how to test it? but its a go from me 🙂

Added a test for this in efa4fd1 on the OpenAPIController, as the new system using OpenAPIRenderPlugin (JsonRenderPlugin and YamlRenderPlugin) does not have this issue.

I suspect #2634 is related but it got mistakenly closed due to the nature of this bug, so one more reason to add a test I guess :D

[JacobCoffee]

thanks for contributing again :)