[FIR] add test case on more suspend conversion with more specific implicit type

^KT-62836

compiler/testData/diagnostics/tests/suspendConversion/implicitInvokeFromChildClass.kt

@@ -0,0 +1,14 @@
+// FIR_IDENTICAL
+// IGNORE_DIAGNOSTIC_API
+// ISSUE: KT-62836
+fun box() {
+    useSuspendFunInt(Child())
+}
+
+fun useSuspendFunInt(fn: suspend () -> String): String = ""
+
+abstract class Test : () -> String
+
+open class Child: Test() {
+    override fun invoke() = "OK"
+}