Fix Up GitHub Release Importer

What does this MR do?

Fix up the Gitlab::GithubImport::Importer::ReleasesImporter.

• Set the GitLab release.updated_at to the GitHub release's created_at.
• Set the GitLab release.name to the GitHub release name.

The GitHub V3 API does not appear to return an updated_at field. (https://developer.github.com/v3/repos/releases/)

This is probably at least part of the reason for the releases on production that do not have an updated_at value. (#27638 (comment 215716638))

Relevant Issue: #27638 (closed)

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team