unique: use runtime.AddCleanup instead of runtime.SetFinalizer

Replace the usage of runtime.SetFinalizer with runtime.AddCleanup in
tests.

Updates #70907

Change-Id: I0d91b6af9643bde278215318f6176277373ddd19
Reviewed-on: https://go-review.googlesource.com/c/go/+/649458
Reviewed-by: Michael Knyszek <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: cagedmantis

src/unique/handle_test.go

@@ -124,12 +124,12 @@ func checkMapsFor[T comparable](t *testing.T, value T) {
 func TestMakeClonesStrings(t *testing.T) {
 	s := strings.Clone("abcdefghijklmnopqrstuvwxyz") // N.B. Must be big enough to not be tiny-allocated.
 	ran := make(chan bool)
-	runtime.SetFinalizer(unsafe.StringData(s), func(_ *byte) {
-		ran <- true
-	})
+	runtime.AddCleanup(unsafe.StringData(s), func(ch chan bool) {
+		ch <- true
+	}, ran)
 	h := Make(s)
 
-	// Clean up s (hopefully) and run the finalizer.
+	// Clean up s (hopefully) and run the cleanup.
 	runtime.GC()
 
 	select {