Add test for KT-51499 (occurs in FE10, already fixed in FIR)

compiler/testData/diagnostics/testsWithStdLib/experimental/fileOptInSuppressesOverride.kt

@@ -0,0 +1,16 @@
+@file:OptIn(Marker::class)
+
+@RequiresOptIn
+@Target(AnnotationTarget.CLASS, AnnotationTarget.FUNCTION)
+annotation class Marker
+
+@Marker
+fun experimental() {}
+
+interface MyInterface {
+    fun execute()
+}
+
+class MyClass : MyInterface {
+    override fun execute() = <!OPT_IN_USAGE_ERROR!>experimental<!>()
+}