Swift: Fix test by including the 'allowParameterReturnInSelf' hook from the variable capture library.

swift/ql/lib/codeql/swift/dataflow/internal/DataFlowPrivate.qll

@@ -1387,7 +1387,12 @@ predicate additionalLambdaFlowStep(Node nodeFrom, Node nodeTo, boolean preserves
  * One example would be to allow flow like `p.foo = p.bar;`, which is disallowed
  * by default as a heuristic.
  */
-predicate allowParameterReturnInSelf(ParameterNode p) { none() }
+predicate allowParameterReturnInSelf(ParameterNode p) {
+  exists(Callable c |
+    c = p.(ParameterNodeImpl).getEnclosingCallable().asSourceCallable() and
+    CaptureFlow::heuristicAllowInstanceParameterReturnInSelf(c)
+  )
+}
 
 /** An approximated `Content`. */
 class ContentApprox = Unit;

swift/ql/test/library-tests/dataflow/capture/closures.swift

@@ -187,5 +187,5 @@ func multi() {
   var y = source("multi", 1)
   var f = { () in x = y }
   f()
-  sink(x) // $ MISSING: hasValueFlow=multi
+  sink(x) // $ hasValueFlow=multi
 }