Skip quarantined web_terminal_spec in most pipelines

What does this MR do and why?

Describe in detail what your merge request does and why.

Skips running web_terminal_spec in most pipelines except main where quarantined jobs are manual. The test is quarantined due to a known bug (#331711 (closed)) and fails constantly. It led to multiple failure issues and comments being created by Gitlab QA Bot so we need to stop running this test by default to reduce the noise, we are still leaving an option of running it on main manually if needed.

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