Small change in instanceofs integration to account for the slightly…

… different boxing semantics under javac.

In conditionals that need boxing, e.g.

```
int m, n;
...
Object o = b ? m : n;

```

the javac frontend expresses the conditional as returning `Object` expressing that the boxing occurs as if written:

```
int m, n;
...
Object o = b ? (Object) m : (Object) n;

```

PiperOrigin-RevId: 702100822

transpiler/javatests/com/google/j2cl/integration/java/instanceofs/Main.java

@@ -97,7 +97,6 @@ default void dummy(int i) {}
 
   private static class Implementor implements ChildInterface, GenericInterface<String> {}
 
-  @SuppressWarnings("cast")
   private static void testInstanceOf_array() {
     // TODO(b/184675805): Enable for Wasm when array metadata is fully implemented.
     if (isWasm()) {
@@ -379,7 +378,7 @@ private static void testInstanceOf_patternVariable() {
     String hello = "hello";
     Object o = hello;
     assertTrue(o instanceof String s && s.length() == hello.length());
-    assertEquals(hello.length(), o instanceof String s ? s.length() : 0);
+    assertTrue(hello.length() == (o instanceof String s ? s.length() : 0));
 
     String bye = "bye";
     o = bye;