Update dependency org.rundeck:rundeck-core to v6.0.0-SNAPSHOT

Author: renovate[bot]

gradle/libs.versions.toml

@@ -1,7 +1,7 @@
 [versions]
 nexusPublish = "2.0.0"
 freemarker = "2.3.34"
-rundeckCore = "6.0.0-alpha1-20260407"
+rundeckCore = "6.0.0-SNAPSHOT"
 axionRelease = "1.21.2"
 # Security overrides for transitive dependencies
 commonsLang3 = "3.20.0"