Fix flaky e2e login step

[annemirasol]

Changes proposed in this Pull Request:

We've been getting a lot of login-related failures for our e2e tests, due to timeouts from waiting for networkidle. Playwright officially discourages the use of networkidle in waitForLoadState (https://playwright.dev/docs/api/class-page#page-wait-for-load-state)

'networkidle' - DISCOURAGED wait until there are no network connections for at least 500 ms. Don't use this method for testing, rely on web assertions to assess readiness instead.

This PR tweaks our login step to wait for load, and use web-first assertions instead of waiting for networkidle.

Testing instructions

Check that e2e tests are green.

---

• Covered with tests (or have a good reason not to test in description ☝️)
• Tested on mobile (or does not apply)

Changelog entry

• This Pull Request does not require a changelog entry. (Comment required below)

Changelog Entry Comment

Comment

Post merge

• Added testing instructions to the Release Testing Instructions wiki page (or does not apply)
• Added the needs docs label (or does not apply)
• Included this PR in the Release Thread scope (or does not apply)

[diegocurbelo]

LGTM 🚢