Address review comments

python/ql/lib/semmle/python/dataflow/new/internal/TaintTrackingPrivate.qll

@@ -188,7 +188,9 @@ predicate containerStep(DataFlow::Node nodeFrom, DataFlow::Node nodeTo) {
     exists(DataFlow::Content c | c = contentSet.getAReadContent() |
       c instanceof DataFlow::TupleElementContent or
       c instanceof DataFlow::DictionaryElementContent or
-      c instanceof DataFlow::DictionaryElementAnyContent
+      c instanceof DataFlow::DictionaryElementAnyContent or
+      c instanceof DataFlow::ListElementContent or
+      c instanceof DataFlow::SetElementContent
     )
   )
 }

python/ql/lib/semmle/python/frameworks/Stdlib.qll

@@ -4983,10 +4983,6 @@ module StdlibPrivate {
         // For code like `" ".join([name])`
         input = "Argument[0,iterable:].ListElement" and
         preservesValue = true
-        or
-        // For code like `" ".join(name)`
-        input = "Argument[0,iterable:]" and
-        preservesValue = false
       ) and
       output = "ReturnValue"
     }