Use python -m tox instead of just tox

This way, macros can use whatever Python has tox module available
instead of only the main one which owns /usr/bin/tox.

macros.pyproject

@@ -92,5 +92,5 @@ TOX_TESTENV_PASSENV="${TOX_TESTENV_PASSENV:-*}" \\
 PATH="%{buildroot}%{_bindir}:$PATH" \\
 PYTHONPATH="${PYTHONPATH:-%{buildroot}%{python3_sitearch}:%{buildroot}%{python3_sitelib}}" \\
 HOSTNAME="rpmbuild" \\
-tox --current-env -q --recreate -e "%{-e:%{-e*}}%{!-e:%{toxenv}}" %{?*}
+%{__python3} -m tox --current-env -q --recreate -e "%{-e:%{-e*}}%{!-e:%{toxenv}}" %{?*}
 }

pyproject_buildrequires.py

@@ -219,7 +219,8 @@ def generate_tox_requirements(toxenv, requirements):
     requirements.check(source='tox itself')
     with tempfile.NamedTemporaryFile('r') as depfile:
         r = subprocess.run(
-            ['tox', '--print-deps-to-file', depfile.name, '-qre', toxenv],
+            [sys.executable, '-m', 'tox', '--print-deps-to-file',
+             depfile.name, '-qre', toxenv],
             check=False,
             encoding='utf-8',
             stdout=subprocess.PIPE,