Test against Gradle 8.9

Author: ajoberstar

reckon-gradle/stutter.lockfile

@@ -1,4 +1,4 @@
 # DO NOT MODIFY: Generated by Stutter plugin.
-java11=7.0.2,7.6.4,8.0.2,8.6
-java17=7.3.3,7.6.4,8.0.2,8.6
-java21=8.4,8.6
+java11=7.0.2,7.6.4,8.0.2,8.9,8.10-rc-1
+java17=7.3.3,7.6.4,8.0.2,8.9,8.10-rc-1
+java21=8.4,8.9,8.10-rc-1