[Gradle] Limit language version for tests providing Gradle plugins

#KT-60588 In Progress

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/kotlinPluginDepsInBuildSrc/buildSrc/build.gradle.kts

@@ -12,4 +12,10 @@ allprojects {
     dependencies {
         implementation("org.jetbrains.kotlin:kotlin-gradle-plugin-api:$kotlin_version")
     }
+}
+
+tasks.named<org.jetbrains.kotlin.gradle.tasks.KotlinCompile>("compileKotlin").configure {
+    compilerOptions {
+        languageVersion.set(org.jetbrains.kotlin.gradle.dsl.KotlinVersion.KOTLIN_1_9)
+    }
 }