Backport fix staking benchmark (#6463) to stable 2412 and disable flaky tests

[gui1117]

Found by @ggwpez

Fix staking benchmark, error was introduced when migrating to v2: #6025

Also disable flaky tests similar to #6749:

• zombienet-polkadot-functional-0017-sync-backing
• zombienet-polkadot-elastic-scaling-0002-elastic-scaling-doesnt-break-parachains

[github-actions]

This pull request is amending an existing release. Please proceed with extreme caution,
as to not impact downstream teams that rely on the stability of it. Some things to consider:

• Backports are only for 'patch' or 'minor' changes. No 'major' or other breaking change.
• Should be a legit fix for some bug, not adding tons of new features.
• Must either be already audited or not need an audit.

Emergency Bypass

If you really need to bypass this check: add validate: false to each crate
in the Prdoc where a breaking change is introduced. This will release a new major
version of that crate and all its reverse dependencies and basically break the release.

[gui1117]

I forced push because I needed to sign the commits

[gui1117]

merging is blocked: The base branch does not allow updates. But can we merge it still? the benchmark doesn't make any sense without this PR.

maybe I am wrong, let's trigger CI again

[gui1117]

I can't make the test continuous-integration/gitlab-zombienet-polkadot-functional-0017-sync-backing pass.

[gui1117]

CI is finally green, maybe merging is blocked for backport now.

[gui1117]

To backport to 2412-1 should it still be merged into the 2412 branch?

[gui1117]

@paritytech/release-engineering This PR can be merged or closed