Fix log assertion in BeanOutputConverterTest to use Java 17

Updated the test to assert log size explicitly before accessing the first log entry. This ensures the test is more robust and avoids potential issues with accessing logs unexpectedly.

Signed-off-by: Konstantin Pavlov <{ID}+{username}@users.noreply.github.com>

Author: Konstantin Pavlov

spring-ai-core/src/test/java/org/springframework/ai/converter/BeanOutputConverterTest.java

@@ -158,7 +158,8 @@ void convertClassType() {
 		void failToConvertInvalidJson() {
 			var converter = new BeanOutputConverter<>(TestClass.class);
 			assertThatThrownBy(() -> converter.convert("{invalid json")).hasCauseInstanceOf(JsonParseException.class);
-			final var loggingEvent = logAppender.list.getFirst();
+			assertThat(logAppender.list).hasSize(1);
+			final var loggingEvent = logAppender.list.get(0);
 			assertThat(loggingEvent.getMessage()).isEqualTo(
 					"Could not parse the given text to the desired target type:{invalid json into " + TestClass.class);
 			assertThat(loggingEvent.getMarkerList()).contains(PII_MARKER);