ci: add Node.js 20 in the test matrix

Reference: https://github.com/nodejs/Release

Author: darrachequesne

.github/workflows/ci.yml

@@ -18,6 +18,7 @@ jobs:
       matrix:
         node-version:
           - 16
+          - 20
 
     steps:
       - name: Checkout repository

test/socket.ts

@@ -852,10 +852,6 @@ describe("socket", () => {
   it("should not crash when messing with Object prototype (and other globals)", (done) => {
     // @ts-ignore
     Object.prototype.foo = "bar";
-    // @ts-ignore
-    global.File = "";
-    // @ts-ignore
-    global.Blob = [];
     const io = new Server(0);
     const socket = createClient(io);