Drop a build dependency on tox

See https://github.com/fedora-eln/eln/issues/126

This is intentionally not conditionalized on %rhel,
as it is simpler this way.

Also, it seems no tests were run at all:

    + /usr/bin/python3 -m tox --current-env -q --recreate -e py311
      py311: OK (0.01 seconds)
      congratulations :) (0.12 seconds)

python-tomli-w.spec

@@ -37,7 +37,10 @@ sed -i '/pytest-randomly/d' tests/requirements.txt
 
 
 %generate_buildrequires
-%pyproject_buildrequires %{?with_check:-t}
+# We intentionally don't use tox here to avoid a dependency on it in ELN/RHEL,
+# the tox deps only list -r tests/requirements.txt anyway and sometimes
+# did not run any tests at all.
+%pyproject_buildrequires %{?with_check:tests/requirements.txt}
 
 
 %build
@@ -52,7 +55,7 @@ sed -i '/pytest-randomly/d' tests/requirements.txt
 %check
 %pyproject_check_import tomli_w
 %if %{with check}
-%tox
+%pytest -v
 %endif