fix electron tests mocking dates (#3599)

fixes #3597 

Changes:
- electron tests: add mocking to `electron.js` for mocking the server
side, before only the browser side was mocked
- publish "/tests/configs" and "/tests/mocks" always in `server.js`,
this reverts a change done with latest release, we need this for
debugging (otherwise you get on the screen that your config has errors
but config check is successful ...)
- revert hotfix in
`tests/configs/modules/calendar/show-duplicates-in-calendar.js`
- fix `tests/configs/modules/calendar/custom.js` to allow events in the
past (~~I don't know how this could work before~~ when testing css
classes `yesterday` and `dayBeforeYesterday` --> it worked before
because the server side did not mock and therefore was not in the past)

CHANGELOG.md

@@ -31,7 +31,7 @@ _This release is scheduled to be released on 2025-01-01._
 - [updatenotification] Fix pm2 using detection when pm2 script is in MagicMirror root folder (#3576)
 - [core] Fix loading node_helper of modules: avoid black screen, display errors and continue loading with next module (#3578)
 - [weather] changed default value for weatherEndpoint of provider openweathermap to "/onecall" (#3574)
-- [calendar] fix one testcase which had a date expired problem..
+- [tests] fix electron tests with mock dates, the mock on server side was missing (#3597)
 
 ## [2.29.0] - 2024-10-01