Re-enable the tests that get skipped on GitHub CI

The [navigation tests that rely on `pagereveal` and `pageswap`](https://github.com/GoogleChromeLabs/view-transitions-toolkit/blob/main/tests/navigation.pw.test.ts) consistently fail when ran in the GitHub CI. Changing the OS from `ubuntu-latest` to `macos-latest` seems to have no effect.

These tests are now manually skipped when GitHub CI is detected: https://github.com/GoogleChromeLabs/view-transitions-toolkit/blob/main/tests/navigation.pw.test.ts#L13-L14

```js
// Skip test when run inside a GitHub action
test.skip(!!process.env.GITHUB_RUN_ID, "Failing in GitHub Actions");
```

Ideally these should be re-enabled but it’s not 100% urgent as tests also run locally before code gets pushed.

Start with tests/navigation.pw.test.ts, especially the pagereveal/pageswap cases and the GITHUB_RUN_ID skip at lines 13-14. Reproduce the failure in GitHub CI and determine why changing the runner OS did not help. Done means the tests are no longer skipped in GitHub Actions and pass there.

Written by the indexing model from the issue text.