Update shared/typeflow/codeql/typeflow/internal/TypeFlowImpl.qll

Co-authored-by: Anders Schack-Mulligen <aschackmull@users.noreply.github.com>

Author: MathiasVP

shared/typeflow/codeql/typeflow/internal/TypeFlowImpl.qll

@@ -19,7 +19,7 @@ module TypeFlow<LocationSig Location, TypeFlowInput<Location> I> {
    * Holds if data can flow from `n1` to `n2` in one step, `n1` is not necessarily
    * functionally determined by `n2`, and `n1` might take a non-null value.
    */
-  predicate joinStep(TypeFlowNode n1, TypeFlowNode n2) { I::joinStep(n1, n2) and not isNull(n1) }
+  private predicate joinStep(TypeFlowNode n1, TypeFlowNode n2) { I::joinStep(n1, n2) and not isNull(n1) }
 
   private predicate anyStep(TypeFlowNode n1, TypeFlowNode n2) { joinStep(n1, n2) or step(n1, n2) }