repo-updater: Make cloned-count ignore gitserver case-sensitivity

Created by: mrnugget

This fixes #4894 by only comparing lower-cased names when calculating the number of not cloned repositories.

The previous fix in #4859 was not enough since now gitserver apparently does return mixed-case repository names.

For me this raises a few questions:

1. Why does gitserver now respond with mixed-case repository names?
2. Why was this change of behaviour triggered when @keegancsmith changed the GHE external service config?
3. Does this break any other setups by making the comparison case-insensitive?

Test plan: go test