downgrade Gradle 9.0 to 8.12 for gretty compatibility

Gretty (including 5.0.1) uses the archivePath property which was
removed in Gradle 9, causing jettyStartWar to fail. Downgrade to
Gradle 8.12 until gretty adds Gradle 9 support.

Author: manolo

gradle/wrapper/gradle-wrapper.properties

@@ -1,6 +1,6 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-9.0-bin.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.12-bin.zip
 networkTimeout=10000
 validateDistributionUrl=true
 zipStoreBase=GRADLE_USER_HOME