Additional commits check does not raise an error without the upstream flag

[renatav]

taf/taf/updater/updater_pipeline.py

Line 1722 in 39d0424

and not self.no_upstream

If there are additional commits in target repositories, validation only fails if no_upstream is False. We do need to ignore these errors in some cases, but upstream seems like the wrong flag to associate this with.

Additionally, if there are multiple repositories that contain additional commits, only one error is shown. Collect all errors before raising an error.