test: install matching Chromium in e2e playwright Dockerfile (#904)

## Summary

The e2e `playwright.Dockerfile` does `pip install --force-reinstall -r
requirements.txt`, which can pull a newer Playwright via
`crawlee[playwright]` than the one pre-installed in the
`apify/actor-python-playwright` base image. When that happens, the
matching Chromium binary isn't on disk and the Actor fails at browser
launch with:

```
BrowserType.launch_persistent_context: Executable doesn't exist at /pw-browsers/chromium_headless_shell-1223/chrome-headless-shell-linux64/chrome-headless-shell
```

This broke both `test_playwright_crawler` and
`test_adaptive_playwright_crawler` on master after a fresh
crawlee/playwright release. Failing CI run:
https://github.com/apify/apify-sdk-python/actions/runs/26033470032/job/76525272306

## Fix

Run `playwright install chromium` after the pip force-reinstall so the
browser binary always matches the just-installed Playwright version,
regardless of how stale the base image's bundled Chromium is.