Smoke test for project snippet

What does this MR do?

Adds a smoke test for creating a project snippet. We already have a smoke test for personal snippets, but a similar quick check for project snippets is missing.

Identified as a test gap in #214761 (closed).

To run the test:

CHROME_HEADLESS=false bundle exec bin/qa Test::Instance::All http://localhost:3000 -- qa/specs/features/browser_ui/3_create/snippet/create_project_snippet_spec.rb

Closes gitlab-org/quality/testcases#813 (closed)

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