manage levels for 'multiple included lists' (#46359)

* manage levels for 'multiple included lists'

fixes #46343

(cherry picked from commit 80d977bac6)

changelogs/fragments/fix_flatten.yml

@@ -0,0 +1,2 @@
+bugfixes:
+    - fix flatten to properly handle multiple lists in lists https://github.com/ansible/ansible/issues/46343

lib/ansible/plugins/filter/core.py

@@ -438,8 +438,8 @@ def flatten(mylist, levels=None):
             if levels is None:
                 ret.extend(flatten(element))
             elif levels >= 1:
-                levels = int(levels) - 1
-                ret.extend(flatten(element, levels=levels))
+                # decrement as we go down the stack
+                ret.extend(flatten(element, levels=(int(levels) - 1)))
             else:
                 ret.append(element)
         else: