Update Dockerfile to use non-root user #2388

Job	Run time
uv-check	9s
flake8	13s
ruff-lint	11s
pymarkdown	9s
pre-commit / autofix-pre-commit	2m 15s
pytest	21s
mypy (package)	31s
mypy (tests)	23s
build-and-publish	51s
release	0s
	5m 3s

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