Add missing libs-snapshot repository declaration

See gh-22640

spring-boot-tests/spring-boot-integration-tests/spring-boot-launch-script-tests/app/build.gradle

@@ -8,7 +8,7 @@ apply plugin: "io.spring.dependency-management"
 repositories {
 	maven { url "file:${rootDir}/../int-test-maven-repository"}
 	mavenCentral()
-	maven { url "https://repo.spring.io/snapshot" }
+	maven { url "https://repo.spring.io/libs-snapshot" }
 	maven { url "https://repo.spring.io/milestone" }
 }