Introduce a test for the development server. Fix #3718. #383

Job	Run time
Linting (flake8, pydocstyle) (3.11)	14s
Linting (flake8, pydocstyle) (3.11)	14s
Build demo site with base requirements (3.11)	18s
Build demo site with base requirements (3.11)	18s
Nikola tests (Python 3.7 on ubuntu-latest)	1m 53s
Nikola tests (Python 3.7 on ubuntu-latest)	1m 53s
Baseline testing (Python 3.11 on ubuntu-latest)	40s
Baseline testing (Python 3.11 on ubuntu-latest)	34s
Nikola tests (Python 3.8 on ubuntu-latest)	1m 56s
Nikola tests (Python 3.8 on ubuntu-latest)	1m 56s
Nikola tests (Python 3.9 on ubuntu-latest)	2m 1s
Nikola tests (Python 3.9 on ubuntu-latest)	2m 1s
Nikola tests (Python 3.10 on ubuntu-latest)	2m 1s
Nikola tests (Python 3.10 on ubuntu-latest)	2m 1s
Nikola tests (Python 3.11 on ubuntu-latest)	1m 55s
Nikola tests (Python 3.11 on ubuntu-latest)	1m 55s
Nikola tests (Python 3.11 on macos-latest)	2m 30s
Nikola tests (Python 3.11 on macos-latest)	2m 30s
Nikola tests (Python 3.11 on windows-latest)	4m 6s
Nikola tests (Python 3.11 on windows-latest)	4m 6s
	35m 2s

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