[FIR] Only let supertypes of ILTs include Number when it's not unsigned

#KT-64607 Fixed

compiler/testData/diagnostics/tests/unsignedTypes/numberReceiverNotValid.kt

@@ -0,0 +1,18 @@
+// FIR_IDENTICAL
+// WITH_STDLIB
+// LANGUAGE: +ContextReceivers
+// ISSUE: KT-64607
+
+val Number.a get() = ""
+fun Number.b() = ""
+context(Number) val c get() = ""
+context(Number) fun d() = ""
+
+fun test() {
+    2U.<!UNRESOLVED_REFERENCE_WRONG_RECEIVER!>a<!>
+    2U.<!UNRESOLVED_REFERENCE_WRONG_RECEIVER!>b<!>()
+    with (2U) {
+        <!NO_CONTEXT_RECEIVER!>c<!>
+        <!NO_CONTEXT_RECEIVER!>d<!>()
+    }
+}