Python: Solve problems with missing TTupleElementContent

Ruby uses 10 as their number. I considered doing the same, but didn't
really care _too_ much about it 🤷

https://github.com/github/codeql/blob/14cfb82a8c16e15fadc006ae46331302f0341f63/ruby/ql/lib/codeql/ruby/dataflow/internal/DataFlowPrivate.qll#L636

Author: RasmusWL

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

@@ -588,6 +588,11 @@ newtype TContent =
     or
     // Arguments can overflow and end up in the starred parameter tuple.
     exists(any(CallNode cn).getArg(index))
+    or
+    // since flow summaries might use tuples, we ensure that we at least have valid
+    // TTupleElementContent for the 0..7 (7 was picked to match `small_tuple` in
+    // data-flow-private)
+    index in [0 .. 7]
   } or
   /** An element of a dictionary under a specific key. */
   TDictionaryElementContent(string key) {

python/ql/test/experimental/dataflow/summaries-checks/invalid-spec.expected

@@ -1,2 +0,0 @@
-| compiled re.subn | ReturnValue.TupleElement[0] | TupleElement[0] |
-| re.subn | ReturnValue.TupleElement[0] | TupleElement[0] |