Fix tests

Address code review feedback

Fix tests

Closes gitaly#985

The refs hash is used to determine what branches and tags have a commit
as head in the network graph. The previous implementation depended on
Rugged#references. The problem with this implementation was that it
depended on rugged, but also that it iterated over all references and
thus loading more data than needed if for example the project uses CI/CD
environments, Pipelines, or Merge Requests.

Given only refs are checked the network cares about the GraphHelper#refs
method has no need to reject those, simplifying the method.

Closes gitlab-org/gitaly#880

Signed-off-by: Rémy Coutable <remy@rymai.me>

+ address small nitpicks

- Move the exception handling as close to the source as possible to
avoid leaking Psych ahstraction
- Also remove unnecessary rescue all statement from LintsController.
This should not be necessary anymore since any YAML errors should all be
caught by the #validation_message method.

Reset Project's column information in spec/lib/gitlab/background_migration/populate_merge_request_metrics_with_events_data_spec.rb

Signed-off-by: Rémy Coutable <remy@rymai.me>