Added git http requests tests for user with LDAP identity

## What does this MR do?

Added tests to git http request for a user with ldap identity.

## Are there points in the code the reviewer needs to double check?

In order to stick to the way the existing tests are defined in spec files, I have added the new tests in the same spec file that coveres the git http request feature and thus it seems to be a lot of changes in the git_http_spec.rb when looking at the commit git in Gitlab, but the largest change is indentation so please check with a better diff tool (i.e. kdiff3).

Let me know if this is OK with you or do you want to have a new file introduced (i.e. `git_http_ldap_spec.rb`)

## Why was this MR needed?

To increase test coverage and to make sure  the changes that will be introduced by #20820 will not introduce any regressions.

## What are the relevant issue numbers?

#20820

See merge request !6559