remove retry from backers on failed candidate validation (#2182)

Hey guys, as discussed I've changed the name to a more general one
`PvfExecKind`, is this good or too general?
Creating this as a draft, I still have to fix the tests.

Closes #1585

Kusama address: FkB6QEo8VnV3oifugNj5NeVG3Mvq1zFbrUu4P5YwRoe5mQN

---------

Co-authored-by: command-bot <>
Co-authored-by: Marcin S <marcin@realemail.net>

polkadot/node/core/approval-voting/src/tests.rs

@@ -2705,10 +2705,10 @@ async fn handle_double_assignment_import(
 	assert_matches!(
 		overseer_recv(virtual_overseer).await,
 		AllMessages::CandidateValidation(CandidateValidationMessage::ValidateFromExhaustive {
-			exec_timeout_kind,
+			exec_kind,
 			response_sender,
 			..
-		}) if exec_timeout_kind == PvfExecTimeoutKind::Approval => {
+		}) if exec_kind == PvfExecKind::Approval => {
 			response_sender.send(Ok(ValidationResult::Valid(Default::default(), Default::default())))
 				.unwrap();
 		}