Start building against Spring Security 5.7.0 snapshots

See gh-31019

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

@@ -1785,7 +1785,7 @@ bom {
 			]
 		}
 	}
-	library("Spring Security", "5.7.0-RC1") {
+	library("Spring Security", "5.7.0-SNAPSHOT") {
 		prohibit("[6.0.0-M1,)") {
 			because "it uses Spring Framework 6"
 		}