Add the interface types for mutable protos so the object hierarchy ca…

…n diverge as it converges with Immutable Builders.

This should have zero impact because `AbstractMutableMessageLite implements MutableMessageLite`.

#checkreturnvalue

PiperOrigin-RevId: 652576976

core/src/main/java/com/google/errorprone/bugpatterns/checkreturnvalue/ProtoRules.java

@@ -50,7 +50,7 @@ public static ResultUseRule<VisitorState, Symbol> protoBuilders() {
    */
   public static ResultUseRule<VisitorState, Symbol> mutableProtos() {
     return new ProtoRule(
-        isDescendantOfAny(ImmutableSet.of("com.google.protobuf.AbstractMutableMessageLite")),
+        isDescendantOfAny(ImmutableSet.of("com.google.protobuf.MutableMessageLite")),
         "MUTABLE_PROTO");
   }