added possibility to ignore MagicMirror repo in updatenotification (#3002)

was [requested in the
forum](https://forum.magicmirror.builders/topic/17519/updatenotification).

- added possibility to exclude MagicMirror Repo and renamed it from
`default` to `MagicMirror`
- improved getting `behind` in case a hard `git fetch` was already done
- removed test "excludes repo if refs don't match regex" because of
above improvement this case is obsolete
- improved `git fetch --dry-run` with `-n` option to exclude tags (noise
reduction)

CHANGELOG.md

@@ -13,6 +13,7 @@ _This release is scheduled to be released on 2023-04-01._
 
 - Added increments for hourly forecasts in weather module (#2996)
 - Added tests for hourly weather forecast
+- Added possibility to ignore MagicMirror repo in updatenotification module
 
 ### Removed