Improve handling of JS logging in headless runner in order to avoid losing logs
and errors e.g. the issue fixed by odoo/odoo#41231 passed because it occurred
during module loading, which happens during initial page loading (browser_js >
navigate_to > _websocket_wait_event), which ignored logs (and exceptions though
here it's a console.error log), and as a result reported no failure (and would
simply miss that specific test as well as every test following it).

This requires additional modifications as we have a fair amount of silent
failures (exceptions or logging.error calls) at the moment:

- downgrade one error to a warning (which becomes an info at the python level)
- cleanup some synthetic / mock errors to better match what comes over RPC (and avoid transient or setup failures)
- tours which end in an action, leading to JS code executing during browser cleanup (and blowing up)
  - if the last step triggers a default (implicit) run, replace by a no-op
  - fix tours for which that does not work by either modifying the last step or adding an additional check step

closes odoo/odoo#41334

Related: odoo/enterprise#7771
Signed-off-by: Xavier Morel (xmo) <xmo@odoo.com>