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

prdoc/pr_6475.prdoc

@@ -0,0 +1,8 @@
+title: Fix staking benchmark
+doc:
+- audience: Runtime Dev
+  description: 'Fix staking benchmark, error was introduced when migrating to v2:
+    https://github.com/paritytech/polkadot-sdk/pull/6025'
+crates:
+- name: pallet-staking
+  bump: patch

substrate/frame/staking/src/benchmarking.rs

@@ -975,20 +975,22 @@ mod benchmarks {
 	) -> Result<(), BenchmarkError> {
 		// number of nominator intention.
 		let n = MaxNominators::<T>::get();
+		create_validators_with_nominators_for_era::<T>(
+			v,
+			n,
+			MaxNominationsOf::<T>::get() as usize,
+			false,
+			None,
+		)?;
+
+		let targets;
 
 		#[block]
 		{
-			create_validators_with_nominators_for_era::<T>(
-				v,
-				n,
-				MaxNominationsOf::<T>::get() as usize,
-				false,
-				None,
-			)?;
+			// default bounds are unbounded.
+			targets = <Staking<T>>::get_npos_targets(DataProviderBounds::default());
 		}
 
-		// default bounds are unbounded.
-		let targets = <Staking<T>>::get_npos_targets(DataProviderBounds::default());
 		assert_eq!(targets.len() as u32, v);
 
 		Ok(())