Replace poetry lock --check with poetry check --lock (#304)

Poetry 1.6.0 deprecated `poetry lock --check` python-poetry/poetry#8015

tox.ini

@@ -48,7 +48,7 @@ allowlist_externals =
 commands_pre =
     poetry install --only lint
 commands =
-    poetry lock --check
+    poetry check --lock
     # uncomment the following line if this charm owns a lib
     # codespell {[vars]lib_path}
     poetry run codespell {[vars]all_path}