Merge pull request #1744 from dbungert/tox-but-faster

tox: use skip_install to speed up black/isort

tox.ini

@@ -2,17 +2,18 @@
 envlist =
     black
     isort
-recreate = True
 
 [testenv]
 basepython = python3
 
 [testenv:black]
 deps = black ~= 23.0
+skip_install = True
 commands = {envpython} -m black \
     {posargs:console_conf subiquity subiquitycore system_setup}
 
 [testenv:isort]
 deps = isort == 5.12.0
+skip_install = True
 commands = {envpython} -m isort \
     {posargs:console_conf subiquity subiquitycore system_setup}