make ctx.spawn blocking (#3337)

* make spawn sync

* improve error type

polkadot/node/network/availability-distribution/src/pov_requester/mod.rs

@@ -76,7 +76,6 @@ where
 		.with_validator_index(from_validator)
 		.with_relay_parent(parent);
 	ctx.spawn("pov-fetcher", fetch_pov_job(pov_hash, pending_response.boxed(), span, tx).boxed())
-		.await
 		.map_err(|e| Fatal::SpawnTask(e))?;
 	Ok(())
 }

polkadot/node/network/availability-distribution/src/requester/fetch_task/mod.rs

@@ -189,7 +189,6 @@ impl FetchTask {
 			let (handle, kill) = oneshot::channel();
 
 			ctx.spawn("chunk-fetcher", running.run(kill).boxed())
-				.await
 				.map_err(|e| Fatal::SpawnTask(e))?;
 
 			Ok(FetchTask {