The browser has to be launch with `proxy: 'per-context'` option for the
tests to work on Windows.
Fixes the following:
```
Error: browser.newContext: Browser needs to be launched with the global proxy. If all contexts override the proxy, global proxy will be never used and can be any string, for example "launch({ proxy: { server: 'http://per-context' } })"
at D:\a\playwright\playwright\tests\library\browsercontext-fetch.spec.ts:382:19
```
Dmitry Gozman