[tox] Update doc testenv to account for documentation restructuring * Build doc from `doc` directory. * Use `sphinx-build` directly instead of `make` as this now works and allows to build within .tox temporary environment (instead of doc/_build), preferable for a "test" action. Related to #5447161.

msgid ""
msgstr ""
"MIME-Version: 1.0\n"
"Content-Type: text/plain; charset=UTF-8\n"
"Content-Transfer-Encoding: 8bit\n"
"Generated-By: pygettext.py 1.5\n"
"Plural-Forms: nplurals=2; plural=(n > 1);\n"
"PO-Revision-Date: YEAR-MO-DA HO:MI +ZONE\n"