[stable2503] Backport paritytech#8861 (paritytech#8867)

Backport paritytech#8861 into `stable2503` from ordian.

See the
[documentation](https://github.com/paritytech/polkadot-sdk/blob/master/docs/BACKPORT.md)
on how to use this bot.

<!--
  # To be used by other automation, do not modify:
  original-pr-number: #${pull_number}
-->

Co-authored-by: ordian <noreply@reusable.software>

polkadot/runtime/parachains/src/inclusion/mod.rs

@@ -613,8 +613,12 @@ impl<T: Config> Pallet<T> {
 				}
 			});
 		}
-
-		(weight, freed_cores)
+		// For relay chain blocks, we're (ab)using the proof size
+		// to limit the raw transaction size of `ParaInherent` and
+		// there's no state proof (aka PoV) associated with it.
+		// Since we already accounted for bitfields size, we should
+		// not include `enact_candidate` PoV impact here.
+		(weight.set_proof_size(0), freed_cores)
 	}
 
 	/// Process candidates that have been backed. Provide a set of