Request Headers are not used in Browser Steps

## Description

When using "Browser Steps", the custom HTTP request headers from the "Request" tab are not sent.

Version: v0.45.14 (self-hosted via docker on a x86_64 Debian Linux)

## How to reproduce

1. Create a new watch for https://www.deviceinfo.me/ or https://myhttpheader.com/
2. At *Request*, choose *Playwright Chromium*.
3. Still at *Request*, click on *Show advanced options*.
4. Add a custom User-Agent in the *Request headers* field.
5. Go to *Browser Steps* and press Play.
6. Scroll down to where it shows both the User-Agent and the HTTP headers.

The custom headers are applied when doing a normal diff/watch. But they are not applied in the *Browser steps*. They seem to be applied to the *Visual Filter Selector* (or maybe the *Visual Filter Selector* uses a cached version that was fetched with the correct custom headers).

Unfortunately, [some sites break when using the *HeadlessChrome* User-Agent](https://github.com/microsoft/playwright/issues/27600) (see #2051). Thus, not only I need this feature, but also I expected the custom headers to be sent on all kinds of requests.

## Desktop

- OS: Manjaro Linux (not relevant)
- Browser: Firefox (not relevant)

(Bonus mini-question: Is there any other place to set a custom User-Agent?)