fix(deps): update dependency org.junit:junit-bom to v6

Author: elastic-renovate-prod[bot]

gradle/libs.versions.toml

@@ -2,7 +2,7 @@
 shadow = "9.2.2"
 jib = "3.4.5"
 spotless = "8.0.0"
-junit = "5.13.4"
+junit = "6.0.0"
 autoservice = "1.1.1"
 log4j2 = "2.25.2"