fix types

Author: pi0

src/stream/readable.ts

@@ -4,7 +4,7 @@ import type { BufferEncoding, Callback } from "../_internal/types";
 import { createNotImplementedError } from "../_internal/utils";
 
 export class Readable extends EventEmitter implements NodeStream.Readable {
-  override __unenv__ = {};
+  __unenv__ = {};
 
   readonly readableEncoding: BufferEncoding | null = null;
   readonly readableEnded: boolean = true;

src/stream/writable.ts

@@ -4,7 +4,7 @@ import { Buffer } from "node-mock-http/_polyfill/buffer";
 import type { BufferEncoding, Callback } from "../_internal/types";
 
 export class Writable extends EventEmitter implements NodeStream.Writable {
-  override __unenv__ = {};
+  __unenv__ = {};
 
   readonly writable: boolean = true;
   writableEnded: boolean = false;