Fix passenv setting for tox.ini

In tox 4.0 `passenv` is required to be one per-line, or comma-separated.

tox.ini

@@ -30,7 +30,11 @@ commands =
     doctesting: {env:_PYTEST_TOX_COVERAGE_RUN:} pytest --doctest-modules --pyargs _pytest
     coverage: coverage combine
     coverage: coverage report -m
-passenv = USER USERNAME COVERAGE_* PYTEST_ADDOPTS TERM SETUPTOOLS_SCM_PRETEND_VERSION_FOR_PYTEST
+passenv =
+    COVERAGE_*
+    PYTEST_ADDOPTS
+    TERM
+    SETUPTOOLS_SCM_PRETEND_VERSION_FOR_PYTEST
 setenv =
     _PYTEST_TOX_DEFAULT_POSARGS={env:_PYTEST_TOX_POSARGS_DOCTESTING:} {env:_PYTEST_TOX_POSARGS_LSOF:} {env:_PYTEST_TOX_POSARGS_XDIST:}
 
@@ -93,7 +97,8 @@ commands =
 [testenv:regen]
 changedir = doc/en
 basepython = python3
-passenv = SETUPTOOLS_SCM_PRETEND_VERSION_FOR_PYTEST
+passenv =
+    SETUPTOOLS_SCM_PRETEND_VERSION_FOR_PYTEST
 deps =
     dataclasses
     PyYAML
@@ -161,7 +166,10 @@ commands = python scripts/prepare-release-pr.py {posargs}
 description = create GitHub release after deployment
 basepython = python3
 usedevelop = True
-passenv = GH_RELEASE_NOTES_TOKEN GITHUB_REF GITHUB_REPOSITORY
+passenv =
+    GH_RELEASE_NOTES_TOKEN
+    GITHUB_REF
+    GITHUB_REPOSITORY
 deps =
     github3.py
     pypandoc