Improve handling of NotSupportedBrowserException #17915

Description:

fixes #17738 Don't log an error when not supported browser is used

To reproduce the error (before the changes in this ticket):

• Monitor the server (e.g. Apache) error log, e.g. tail -f error_log
• Do a GET on matomo with an unsupported browser version e.g. Firefox < version 32, e.g.
  wget -U "Mozilla/5.0 (Windows NT 5.1; rv:2.0) Gecko/20100101 Firefox/4.0" --no-check-certificate https://127.0.0.1/matomo/

To test the fix:

• Repeat the steps to reproduce above - you should not see the message in the error log.
• In config.ini.php, set loglevel=DEBUG (the default is WARN):

  [log]
  log_level = DEBUG

• Repeat the steps to reproduce above - you should now see the message in the error log.

Review

• [ ] Functional review done
• [ ] Potential edge cases thought about (behavior of the code with strange input, with strange internal state or possible interactions with other Matomo subsystems)
• [ ] Usability review done (is anything maybe unclear or think about anything that would cause people to reach out to support)
• [ ] Security review done see checklist
• [ ] Code review done
• [ ] Tests were added if useful/possible
• [ ] Reviewed for breaking changes
• [ ] Developer changelog updated if needed
• [ ] Documentation added if needed
• [ ] Existing documentation updated if needed

If you don't want this PR to be closed automatically in 28 days then you need to assign the label 'Do not close'.

Dealt with in PR #17812

Hm no it's not dealt with after all - re-opening.