Minor. Use coroutine test helpers for inline/diagnostics tests

It should help with decreasing test data copy-pasting when
testing against release / pre-release coroutines

compiler/tests-common/tests/org/jetbrains/kotlin/checkers/BaseDiagnosticsTest.kt

@@ -35,6 +35,7 @@ import org.jetbrains.kotlin.config.LanguageVersionSettingsImpl
 import org.jetbrains.kotlin.descriptors.DeclarationDescriptor
 import org.jetbrains.kotlin.diagnostics.*
 import org.jetbrains.kotlin.load.java.InternalFlexibleTypeTransformer
+import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.psi.KtDeclaration
 import org.jetbrains.kotlin.psi.KtFile
 import org.jetbrains.kotlin.resolve.BindingContext
@@ -220,6 +221,8 @@ abstract class BaseDiagnosticsTest : KotlinMultiFileTestWithJava<TestModule, Tes
                 return true
             }
 
+            if (ktFile.name.endsWith("CoroutineUtil.kt") && ktFile.packageFqName == FqName("helpers")) return true
+
             // TODO: report JVM signature diagnostics also for implementing modules
             val jvmSignatureDiagnostics = if (skipJvmSignatureDiagnostics)
                 emptySet<ActualDiagnostic>()