Fix #5079: Gradle Build Failed - Task :utility:kaptGenerateStubsDebug…

…Kotlin FAILED (#5162)

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## Explanation
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Fixes #5079

The error message indicates that there's a compatibility issue with the
Java version being used for the project. The `Unsupported class file
major version 59` suggests that the code in the model.jar (project
:model) file is compiled with a Java version higher than the one being
used by the project.

This PR explicitly set the source and target compatibility to Java 8 for
the project. This ensures that the project uses Java 8, which is
compatible with class files compiled with major version 59 (Java 15).

By making this change, we ensure that the project's Java version aligns
with the Java version used to compile the model.jar file, thus resolving
the compatibility issue and allowing the build process to proceed
without errors.

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model/build.gradle

@@ -38,3 +38,8 @@ sourceSets {
     }
   }
 }
+
+java {
+    sourceCompatibility = JavaVersion.VERSION_1_8
+    targetCompatibility = JavaVersion.VERSION_1_8
+}