Fix incorrect commands registration in test of docs generation

[sfc-gh-pjob]

Pre-review checklist

• I've confirmed that instructions included in README.md are still correct after my changes in the codebase.
• I've added or updated automated unit tests to verify correctness of my new code.
• I've added or updated integration tests to verify correctness of my new code.
• I've confirmed that my changes are working by executing CLI's commands manually on MacOS.
• I've confirmed that my changes are working by executing CLI's commands manually on Windows.
• I've confirmed that my changes are up-to-date with the target branch.
• I've described my changes in the release notes.
• I've described my changes in the section below.

Changes description

• Fixed flaky test of docs generation.
• app_context_holder.app_context = click.get_current_context() from cli_app.py is not invoked when snow --help is used because --help is eager option causing CLI exit before the line called. As the result side effects from previous tests were still visible in app_context_holder.app_context and caused issues in test_docs_generation_output tests. I changed snow --help to just snow.
• This is only a patch which does not resolve the root cause of issue - command registration state shared by tests. This will be improved in SNOW-1747456.

[sfc-gh-pjob]

Closing in favour of #1945