Update libs.versions.toml

Author: fdevans

gradle/libs.versions.toml

@@ -1,7 +1,7 @@
 [versions]
 nexusPublish = "2.0.0"
 freemarker = "2.3.34"
-rundeckCore = "6.0.0-SNAPSHOT"
+rundeckCore = "6.0.0-alpha1-20260407"
 axionRelease = "1.18.16"
 # Security overrides for transitive dependencies
 commonsLang3 = "3.20.0"