use a .lock extension on lockfiles

Author: cognifloyd

lockfiles/flake8 lockfiles/flake8.locklockfiles/flake8 renamed to lockfiles/flake8.lock

@@ -88,7 +88,7 @@ lockfile = "lockfiles/black.lock"
 version = "black==22.3.0"
 
 [flake8]
-lockfile = "lockfiles/flake8"
+lockfile = "lockfiles/flake8.lock"
 version = "flake8==4.0.1" # st2flake8 does not support flake8 v5
 extra_requirements = [
   # license check plugin