Now that SkyKey is an interface, accept Iterable<? extends SkyKey>

A subsequent CL makes TargetPatternKey implement SkyKey, and it's much nicer
if I can pass lists of TargetPatternKey to the various Skyframe APIs.

PiperOrigin-RevId: 162359843
diff --git a/src/test/java/com/google/devtools/build/skyframe/NotifyingHelper.java b/src/test/java/com/google/devtools/build/skyframe/NotifyingHelper.java
index 0ac49e5..c24f54e 100644
--- a/src/test/java/com/google/devtools/build/skyframe/NotifyingHelper.java
+++ b/src/test/java/com/google/devtools/build/skyframe/NotifyingHelper.java
@@ -88,7 +88,7 @@
 
     @Override
     public Map<SkyKey, ? extends NodeEntry> getBatch(
-        @Nullable SkyKey requestor, Reason reason, Iterable<SkyKey> keys)
+        @Nullable SkyKey requestor, Reason reason, Iterable<? extends SkyKey> keys)
         throws InterruptedException {
       return Maps.transformEntries(
           delegate.getBatch(requestor, reason, keys),