Update grails monorepo (#1735)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

gradle.properties

@@ -15,7 +15,7 @@ servletApiVersion=4.0.1
 spockVersion=2.1-groovy-3.0
 springVersion=5.3.27
 caffeineVersion=2.9.3
-grailsVersion=6.0.0-M2
+grailsVersion=6.0.0-M4
 grailsAsyncVersion=4.0.0
 slf4jVersion=1.7.36
 javaParserCoreVersion=3.15.14