Revert "Release 6.0.0-M2"

This reverts commit 5f7c98d700a0b60c6350c350d4edf28b0b9e8f85.

gradle.properties

@@ -3,7 +3,7 @@ springJavaformatVersion=0.0.31
 springBootVersion=2.4.2
 springFrameworkVersion=6.0.0-M2
 openSamlVersion=3.4.6
-version=6.0.0-M2
+version=6.0.0-SNAPSHOT
 kotlinVersion=1.6.20-M1
 samplesBranch=6.0.x
 org.gradle.jvmargs=-Xmx3g -XX:+HeapDumpOnOutOfMemoryError