Add regression test to close #45389

Author: AnthonyLatsis

test/decl/protocol/req/associated_type_inference_operator.swift

@@ -0,0 +1,12 @@
+// RUN: %target-typecheck-verify-swift
+
+struct Box<T> {}
+
+infix operator =*=
+protocol P1 {
+  associatedtype A
+  static func =*= (x: Self, y: Box<A>)
+}
+class C1<A>: P1 {
+  static func =*= (x: C1, y: Box<A>) {}
+}