Increase -jvm-target for Kotlin JVM targets in g3 from 11 to 21.

PiperOrigin-RevId: 878819763

Author: java-team-github-bot

core/src/test/java/com/google/common/truth/ComparisonFailureWithFactsTest.java

@@ -280,7 +280,8 @@ public void serialization_comparisonFailureWithFacts() {
         (ComparisonFailure) makeComparisonFailure(messages, facts, expected, actual, cause);
 
     ComparisonFailure reserializedFailure = reserialize(original);
-    ErrorWithFacts reserialized = (ErrorWithFacts) reserializedFailure;
+    // TODO: b/491194734 - Remove this redundant cast once Kotlin header compilation permits.
+    ErrorWithFacts reserialized = (ErrorWithFacts) ((AssertionError) reserializedFailure);
     assertThat(reserializedFailure).hasMessageThat().isEqualTo(original.getMessage());
     assertThat(reserializedFailure).hasCauseThat().hasMessageThat().isEqualTo(cause.getMessage());
     assertThat(reserialized.facts().get(0).getKey()).isEqualTo("first");