github/workflows: fix selenium-server flakiness (#1062)
github/workflows: fix selenium-server flakiness (#1062)

* github/workflows: fix selenium-server flakiness

The previous code wasn't doing the right thing: it started the server in
background, slept for 3 seconds in background and started the tests.
Adding another `&` after `sleep 3` would make it actually wait 3
seconds, but instead of doing that we use `timeout` and try the
healthcheck endpoint until the server is ready.

Also upgrade selenium-server.

* Wait for up to 1 minute for selenium-server to become ready

According to this failure:
https://github.com/cobrateam/splinter/runs/7091151103?check_suite_focus=true,
30 seconds may not be enough (!!)

In that log specifically, you can see that the last failure is at
2022-06-28 11:06:25, and the server becomes ready at 11:06:26.519. 1
second difference, so hopefully doubling the timeout is enough.
cobrateam/splinter,cobrateam/splinter,cobrateam/splinter