add py313 to tox and break out python env list

Author: mahmoud

tox.ini

@@ -1,12 +1,15 @@
 [tox]
-envlist = py37,py38,py39,py310,py311,py312,pypy3,coverage-report,packaging
+python_envs = py37,py38,py39,py310,py311,py312,py313,pypy3
+envlist = {[tox]python_envs},coverage-report,packaging
 
 [testenv]
 changedir = .tox
 deps = -rrequirements.txt
 commands = coverage run --parallel --rcfile {toxinidir}/.tox-coveragerc -m pytest -vv --doctest-modules {envsitepackagesdir}/glom {posargs}
 
+
 [testenv:coverage-report]
+depends = {[tox]python_envs}
 changedir = .tox
 deps = coverage
 commands = coverage combine --rcfile {toxinidir}/.tox-coveragerc