Upgrade to Jetty 12.0.20

Closes gh-45451

Author: snicoll

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

@@ -966,7 +966,7 @@ bom {
 			]
 		}
 	}
-	library("Jetty", "12.0.19") {
+	library("Jetty", "12.0.20") {
 		group("org.eclipse.jetty.ee10") {
 			bom("jetty-ee10-bom")
 		}