Resolve missing SnippetType argument

What does this MR do?

Adds a missing calls_gitaly: true argument to the SnippetType repo fields so that calls to Gitaly can be made successfully. Without this, we would experience:

RuntimeError (Gitaly is called for field 'sshUrlToRepo' on Types::SnippetType - please either specify a constant complexity or add `calls_gitaly: true` to the field declaration):

This was originally missed because the spec suite has the RequestStore disabled by default, so I've also added coverage that caters for both scenarios.

More context here: #204730 (comment 316123647)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability 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
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done