Remove "Unable to create pipeline" error

What does this MR do and why?

Before this change, two error messages would appear when running a pipeline via commiting a file when the user's account was unverified:

As noted in the associated bug ticket, "If the identity verification step was complete, the error message 'Unable to create pipeline' would be out of date"

The top error is rendered in Vue and and the bottom is in HAML, however we should only be rendering the top error.

After discussion with @furkanayhan it was suggested that we follow the pattern used for the composite_identity_forbidden error in the HAML (what is currently present in this diff),

The change essentially short-circuits the generic error block when @pipeline.user_not_verified? is true to instead render the banner we'd like instead which results in the user seeing this:

References

#556868

How to set up and validate locally

0. Setup IV tooling locally.

ApplicationSetting.current.update!(ci_requires_identity_verification_on_free_plan: true)
::Gitlab::CurrentSettings.update!(telesign_customer_xid: <GET_THIS_FROM_1Password>, telesign_api_key: <GET_THIS_FROM_1Password>)
::Gitlab::CurrentSettings.update!(email_confirmation_setting: 'hard')
::Gitlab::CurrentSettings.update!(require_admin_approval_after_user_signup: false)

1. Make sure you have your gitlab-runner setup and running via gitlab-runner run
2. Commit or run a pipeline on an unverified account
3. Verify you only see the ("verify my identity") message and not a "unable to create pipeline" additional message
4. Complete IV on IV page
5. Confirm your screen looks like this:

MR acceptance checklist

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