ci(actions): pin prod-test action image (#43748)
## Bug
Test(Production) CI fails with error
```
Package libicu66 is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
E: Package 'ttf-unifont' has no installation candidate
E: Package 'ttf-ubuntu-font-family' has no installation candidate
E: Unable to locate package libenchant1c2a
E: Package 'libicu66' has no installation candidate
E: Unable to locate package libvpx6
E: Unable to locate package libwebp6
Failed to install browser dependencies
```
This is due to new release for the runner image (https://github.com/actions/runner-images/issues/6399) now sets ubuntu 22.04 as latest, but playwright have release to support it (https://github.com/microsoft/playwright/issues/13738) but @replayio/playwright seems not picked it up yet (https://github.com/replayio/replay-cli/blob/main/packages/playwright/package.json#L23)
PR tries to pin to known working image (20.04) until dependencies can support new image gracefully.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have a helpful link attached, see [`contributing.md`](https://github.com/vercel/next.js/blob/canary/contributing.md)
## Feature
- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] [e2e](https://github.com/vercel/next.js/blob/canary/contributing/core/testing.md#writing-tests-for-nextjs) tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have a helpful link attached, see [`contributing.md`](https://github.com/vercel/next.js/blob/canary/contributing.md)
## Documentation / Examples
- [ ] Make sure the linting passes by running `pnpm build && pnpm lint`
- [ ] The "examples guidelines" are followed from [our contributing doc](https://github.com/vercel/next.js/blob/canary/contributing/examples/adding-examples.md)
