Improve GitContextTest tests to actually test something

[salimbouch]

Expected behavior

As an IDEasy developer, I want unit tests that actually test whether something is correct or wrong.

Actual behavior

Right now the class GitContextTest has 3 methods (testIsRepositoryUpdateAvailableNoUpdates, testFetchIfNeededRecentFetchHead, testFetchIfNeededOffline) that only check whether an empty initialized variable is empty or not, therefore not really testing anything and just increasing the coverage for no reason.