Point to samples branch 5.8.x

Closes gh-11203

gradle.properties

@@ -5,7 +5,7 @@ springFrameworkVersion=5.3.19
 openSamlVersion=3.4.6
 version=5.8.0-SNAPSHOT
 kotlinVersion=1.6.20
-samplesBranch=5.7.x
+samplesBranch=5.8.x
 org.gradle.jvmargs=-Xmx3g -XX:MaxPermSize=2048m -XX:+HeapDumpOnOutOfMemoryError
 org.gradle.parallel=true
 org.gradle.caching=true