Skip e2e:test-on-cng job in stable branches

What does this MR do and why?

This was initially raised in gitlab-org/quality/quality-engineering/team-tasks#2787 (comment 1984866631).

Skip e2e:test-on-cng job in stable branches

Update .qa:rules:e2e:test-on-cng rule to skip running in stable branches until gitlab-org/quality/quality-engineering&89 (closed) is completed

Related to gitlab-org/quality/quality-engineering/team-tasks#2787 (closed)

MR acceptance checklist

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