For backport MRs, only run e2e:test-on-omnibus-ee on tier 3

What does this MR do and why?

Only runs e2e:test-on-omnibus-ee job for tier 3 backport MR pipelines.

Tier 1 and Tier 2 backport MR pipelines take an average total of ~95m. Removing this job from tier 1 pipelines will effectively halve the tier 1 pipeline runtime. (95m - 48m = 47m (50.5% reduction per-pipeline))

Justification

Given that:

• e2e:test-on-omnibus-ee consumes ~96m of compute time (~48m runtime)
• e2e:test-on-omnibus-ee is already executed on Tier 3 pipelines
• Code changes must be Tier 3 to be merge

It is safe to remove this job from Tier 1 pipelines without compromising quality.

References

Using this test backport:

• ✅ Expect e2e:test-on-omnibus-ee not to exist for pipelinetier-1.
• ✅ Expect e2e:test-on-omnibus-ee to exist for pipelinetier-3.

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.