Improve browser close detection constant timeout

[inancgumus]

Originally posted by @inancgumus in #1442 (comment)

xk6-browser/common/browser.go

Lines 539 to 552 in aa6a1c0

	if !b.browserOpts.isRemoteBrowser {
	var closeErr *websocket.CloseError
	// Using the internal context with a timeout of 10 seconds here since
	// 1. vu context will very likely be closed;
	// 2. there's a chance that the process has died but the connection still
	// thinks it's open.
	toCtx, toCancelCtx := context.WithTimeout(b.browserCtx, time.Second*10)
	defer toCancelCtx()
	err := cdpbrowser.Close().Do(cdp.WithExecutor(toCtx, b.conn))
	if err != nil && !errors.As(err, &closeErr) {
	b.logger.Errorf("Browser:Close", "closing the browser: %v", err)
	}
	}

I worry that we would need to change this whenever a larger timeout is needed. A larger timeout can cause prematurely aborted errors from the engine team. Two hopefully possible solutions:

• Implementing our own Context implementation that automatically cancels when the process is dead
• Making this an environment variable