Add warning about groovyVersion property

Author: jdaugherty

UPGRADE7.md

@@ -25,6 +25,7 @@ Experienced while upgrading modules for Grails 7
         }
 - The `jakarta` package switch means that older libraries using `javax` will need to be updated to use the correct namespace.  The side effect of this change is most grails plugins will likely need updated to be compatible with Grails 7.
 - When migrating a new project to Grails 7, it's advised to generate a stock 7.0 app from [start.grails.org](https://start.grails.org) and compare the project with a grails app generated from the same grails version that your application uses.  This helps catch the dependency clean up that has occurred.  Including the additions of new dependencies.  Note: due to an issue with project resolution the `grails-bom` will need explicitly imported in buildSrc or any project that does not apply the grails gradle plugins (grails-plugin, grails-web, or grails-gsp).  By default, the grails gradle plugins (grails-plugin, grails-web, grails-gsp) will apply the bom automatically.
+- the gradle property `groovyVersion` is being replaced with the upstream spring property name `groovy.version`.  Please update your projects accordingly.
 
 ## NOTE: This document is a draft and the explanations are only highlights and will be expanded further prior to release of 7.0.