fix: downgrade Gradle to 8.1 for ForgeGradle 5.1.x compatibility

Author: Meeuyt

gradle/wrapper/gradle-wrapper.properties

@@ -1,6 +1,6 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-8.12.1-bin.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.1-bin.zip
 networkTimeout=10000
 validateDistributionUrl=true
 zipStoreBase=GRADLE_USER_HOME