Replace ref equality with .equals for SkyFunctionNames

Ref equality for same-name SkyFunctionNames is not guaranteed.

--
MOS_MIGRATED_REVID=100322275
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/SkyFunctions.java b/src/main/java/com/google/devtools/build/lib/skyframe/SkyFunctions.java
index 2698cd7..caec042 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/SkyFunctions.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/SkyFunctions.java
@@ -86,7 +86,7 @@
     return new Predicate<SkyKey>() {
       @Override
       public boolean apply(SkyKey key) {
-        return key.functionName() == functionName;
+        return key.functionName().equals(functionName);
       }
     };
   }