[Gradle] Adjust the MPP test project for KT-34901

Following the resolution of KT-59595, the java plugin is no longer applied in MPP projects. However, the `java-test-fixtures` plugin is currently non-functional due to its reliance on the `java` plugin (https://github.com/gradle/gradle/blob/e95eafb8c43c5cd404bd235fa0a69c58cab6f5d6/subprojects/plugins/src/main/java/org/gradle/api/plugins/JavaTestFixturesPlugin.java#L60).

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/mpp-test-fixtures/build.gradle

@@ -1,5 +1,6 @@
 plugins {
     id("org.jetbrains.kotlin.multiplatform")
+    id("java")
     id("java-test-fixtures")
 }
 
@@ -22,6 +23,6 @@ kotlin {
     }
 }
 
-tasks.named("test").configure {
+tasks.named("jvmTest").configure {
     useJUnitPlatform()
 }