Update grails monorepo to v6.0.0-RC1 (#709)

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

Author: renovate[bot]

gradle.properties

@@ -1,7 +1,7 @@
 assetPipelineVersion=3.3.4
 gebVersion=2.3
 gormVersion=8.0.0-M2
-grailsGradlePluginVersion=6.0.0-M2
+grailsGradlePluginVersion=6.0.0-RC1
 groovyVersion=3.0.11
 h2Version=1.4.200
 hibernate5Version=5.6.15.Final
@@ -15,7 +15,7 @@ micronautVersion=3.8.8
 micronautSpringVersion=4.5.1
 picocliVersion=4.6.3
 projectVersion=8.0.0-SNAPSHOT
-pluginGrailsVersion=6.0.0-M2
+pluginGrailsVersion=6.0.0-RC1
 seleniumSafariDriverVersion=3.14.0
 seleniumVersion=3.14.0
 servletApiVersion=4.0.1