Revert "Release 6.0.0-M6"

This reverts commit c8fa238cfc5c9052efac7fdcb873d3748c227340.

docs/antora.yml

@@ -1,4 +1,3 @@
-'display_version': '6.0.0-M6'
 'name': 'ROOT'
-'prerelease': 'true'
-'version': '6.0.0-M6'
+'prerelease': '-SNAPSHOT'
+'version': '6.0.0'

gradle.properties

@@ -3,7 +3,7 @@ springJavaformatVersion=0.0.34
 springBootVersion=2.4.2
 springFrameworkVersion=6.0.0-SNAPSHOT
 openSamlVersion=3.4.6
-version=6.0.0-M6
+version=6.0.0-SNAPSHOT
 kotlinVersion=1.7.10
 samplesBranch=main
 org.gradle.jvmargs=-Xmx3g -XX:+HeapDumpOnOutOfMemoryError