FIR: Fix overridability of Kotlin vararg from Java

compiler/testData/diagnostics/tests/j+k/types/varargOverride.kt

@@ -0,0 +1,20 @@
+// SKIP_TXT
+// FIR_IDENTICAL
+// FILE: A.java
+
+import org.jetbrains.annotations.NotNull;
+
+public interface A extends B {
+    void foo(@NotNull String... value);
+}
+
+// FILE: main.kt
+interface B {
+    fun foo(vararg x: String) {}
+}
+
+fun main(a: A) {
+    a.foo()
+    a.foo("1")
+    a.foo("2", "3")
+}