Ensure PATH env matches CI locally (#45376)

Since the tests are run with `pnpm test` locally this adds the repo's
`node_modules/.bin` to the PATH env variable although in CI `node
run-tests.js` is used which doesn't augment PATH like this so this
strips these from the env when running isolated tests to match behavior.

x-ref: [slack
thread](https://vercel.slack.com/archives/C04DUD7EB1B/p1674913457101449)

test/lib/next-modes/base.ts

@@ -65,6 +65,17 @@ export class NextInstance {
 
   constructor(opts: NextInstanceOpts) {
     Object.assign(this, opts)
+
+    this.env = {
+      ...this.env,
+      // remove node_modules/.bin repo path from env
+      // to match CI $PATH value and isolate further
+      PATH: process.env.PATH.split(path.delimiter)
+        .filter((part) => {
+          return !part.includes(path.join('node_modules', '.bin'))
+        })
+        .join(path.delimiter),
+    }
   }
 
   protected async writeInitialFiles() {