Improve non-root site handling of nikola auto. Fix #3715. (PR#3727) #395

Job	Run time
Linting (flake8, pydocstyle) (3.11)	14s
Build demo site with base requirements (3.11)	19s
Nikola tests (Python 3.7 on ubuntu-latest)	1m 45s
Baseline testing (Python 3.11 on ubuntu-latest)	41s
Nikola tests (Python 3.8 on ubuntu-latest)	1m 56s
Nikola tests (Python 3.9 on ubuntu-latest)	1m 45s
Nikola tests (Python 3.10 on ubuntu-latest)	1m 56s
Nikola tests (Python 3.11 on ubuntu-latest)	1m 49s
Nikola tests (Python 3.11 on macos-latest)	3m 32s
Nikola tests (Python 3.11 on windows-latest)	3m 53s
	17m 50s

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