Fix toolchain test fails jvm target validation

Happens after changes for KT-54933 was merged earlier than for KT-55004.

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/kotlin/org/jetbrains/kotlin/gradle/KotlinJavaToolchainTest.kt

@@ -668,6 +668,17 @@ class KotlinJavaToolchainTest : KGPBaseTest() {
             gradleVersion = gradleVersion,
             buildOptions = defaultBuildOptions.copy(logLevel = LogLevel.DEBUG)
         ) {
+            //language=Groovy
+            subProject("lib").buildGradle.appendText(
+                """
+                |
+                |tasks.named("compileJava", JavaCompile) {
+                |    targetCompatibility = JavaVersion.VERSION_11
+                |    sourceCompatibility = JavaVersion.VERSION_11
+                |}
+                """.trimMargin()
+            )
+
             //language=Groovy
             buildGradle.appendText(
                 """