fix(sio): do not throw when calling io.close() on a stopped server

Following [1], calling both `io.close()` and `httpServer.close()` would throw an ERR_SERVER_NOT_RUNNING exception, which was not the case before.

Related: #5431

[1]: bb0b480

Author: darrachequesne

packages/socket.io/lib/index.ts

@@ -831,14 +831,13 @@ export class Server<
     restoreAdapter();
 
     if (this.httpServer) {
-      await new Promise<void>((resolve, reject) => {
+      return new Promise<void>((resolve) => {
         this.httpServer.close((err) => {
           fn && fn(err);
           if (err) {
-            reject(err);
-          } else {
-            resolve();
+            debug("server was not running");
           }
+          resolve();
         });
       });
     } else {

packages/socket.io/test/close.ts

@@ -70,6 +70,27 @@ describe("close", () => {
     });
   });
 
+  it("should not throw when the underlying HTTP server is not running (callback)", (done) => {
+    const httpServer = createServer();
+    const io = new Server(httpServer);
+
+    io.close((err) => {
+      expect((err as Error & { code: string }).code).to.eql(
+        "ERR_SERVER_NOT_RUNNING",
+      );
+      done();
+    });
+  });
+
+  it("should not throw when the underlying HTTP server is not running (Promise)", (done) => {
+    const httpServer = createServer();
+    const io = new Server(httpServer);
+
+    io.close()
+      .then(() => done())
+      .catch((e) => done(e));
+  });
+
   describe("graceful close", () => {
     function fixture(filename) {
       return (