Prohibit upgrades to REST Assured 4.3

REST Assured 4.3.x requires Groovy 3 that we can't yet upgrade to as
there is no compatibile GA of Spock.

This commit prohibits upgrades to 4.3 so that Bomr ignores the possible
upgrade.

See gh-22303

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

@@ -1322,6 +1322,9 @@ bom {
 		}
 	}
 	library("REST Assured", "4.2.1") {
+		prohibit("[4.3.0,)") {
+			because "it requires Groovy 3"
+		}
 		group("io.rest-assured") {
 			modules = [
 				"json-path",