changelog: :ref:package_env`` cannot resolve (tox target, no local label) #14818

The changelog entry for #13933 references :ref:package_env`` twice (doc/en/changelog.rst lines 469 and 484 at f306da7):

version string can be passed into its :ref:package_env through
the SETUPTOOLS_SCM_PRETEND_VERSION_FOR_PYTEST environment
variable as a part of the release process

package_env is a tox setting, and no label with that name exists in pytest's own docs, so the plain :ref: cannot resolve locally; the Sphinx build warns and the rendered changelog carries an unresolved reference.

Two possible fixes, whichever fits your intersphinx setup:

• :external+tox:ref:package_env`` if tox is (or can be) in intersphinx_mapping
• a plain link: `package_env <https://tox.wiki/en/latest/config.html#package_env>`_

Both occurrences carry the same towncrier-generated text, so one correction at the source covers both.

Found by amiss while validating its Sphinx :ref: resolution against the pytest docs tree.