Properly load LaTeX themes when `theme` or `import` is used in `\usepackage[...]{markdown}` #3010

Job	Run time
Style check (Bash)	6s
Style check (Python)	23s
Style check (Line length)	45s
Style check (Lua)	40s
Style check (Markdown)	52s
Style check (Tabs and spaces)	4s
Type check (Python)	43s
Build Docker image (latest)	12m 23s
Test Docker image (latest)	45m 57s
Automatically merge pull request	2s
Publish artefacts and create a prerelease	0s
Publish Docker image	0s
	1h 1m 55s

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