Upgrade to Jetty 9.4.42.v20210604

Closes gh-26838

spring-boot-project/spring-boot-dependencies/build.gradle

@@ -883,7 +883,7 @@ bom {
 			]
 		}
 	}
-	library("Jetty", "9.4.41.v20210516") {
+	library("Jetty", "9.4.42.v20210604") {
 		prohibit("[11.0.0-alpha0,)") {
 			because "it uses the jakarta.* namespace"
 		}