Add Swift 5.9

Author: fwal

__tests__/swift-versions.test.ts

@@ -28,7 +28,7 @@ describe("swift version resolver", () => {
 
   it("identifies X versions", async () => {
     const version = await versions.verify("5", macOS);
-    expect(version).toBe("5.8.1");
+    expect(version).toBe("5.9");
   });
 
   it("identifies versions based on system", async () => {

src/swift-versions.ts

@@ -3,6 +3,7 @@ import * as core from "@actions/core";
 import { System, OS } from "./os";
 
 const VERSIONS_LIST: [string, OS[]][] = [
+  ["5.9", [OS.MacOS, OS.Ubuntu]],
   ["5.8.1", [OS.MacOS, OS.Ubuntu]],
   ["5.8", [OS.MacOS, OS.Ubuntu]],
   ["5.7.3", [OS.MacOS, OS.Ubuntu]],