Small improvements to tox configuration (#343)

Had issues running tox locally which in the end were unrelated to the
configuration. But in the meantime I learned some better practices for
tox, which I implemented in this PR.

tox.ini

@@ -13,33 +13,41 @@ python =
     3.11: py311
 
 [testenv:pre-commit]
+skip_install=true
 allowlist_externals=
     pre-commit
 commands=pre-commit run --all-files --show-diff-on-failure
 
 [testenv:check-licenses]
+skip_install=true
 deps=
     liccheck>=0.7.3,<0.8
-commands=
+allowlist_externals=
+    poetry
+commands_pre=
     poetry lock
     poetry install --all-extras
     poetry show
     poetry export -f requirements.txt --output /tmp/requirements.txt
+commands=
     poetry run liccheck -s license_strategy.ini -r /tmp/requirements.txt -l PARANOID
 
-[testenv]
+[testenv:py{38,39,310,311}]
 setenv=PYTHONPATH = {toxinidir}:{toxinidir}
+skip_install=true
 deps=
     pytest>=7.4.0,<8
     pytest-cov>=4.1.0,<5
 allowlist_externals=
     poetry
     /bin/bash
     /usr/bin/bash
-commands=
+commands_pre=
     bash ./scripts/pre-build.sh
     poetry lock
     poetry install --all-extras
     poetry show
+commands=
     poetry run python -m pytest tests -vv --cov fondant --cov-report term-missing
+commands_post=
     bash ./scripts/post-build.sh