Log spam when enable parachain::pvf=trace

[xlc]

parachain::pvf=trace is required to diagnostic para block validation issue. However this log prints the entire head data, which is a ridiculously large binary blob and make debugging very hard. We start observing this issue since 0.9.12.

2021-11-04 01:06:18.631 DEBUG tokio-runtime-worker parachain::pvf: job finished. validation_code_hash=0x9fe0c149def566a0326e2443f4a73232e5fb2e46ea5337fd3aedbd79f11d7c6f worker_rip=false result=Ok(ValidationResult { head_data: HeadData([18

polkadot/node/core/pvf/src/execute/queue.rs

Lines 247 to 253 in 8962e04

	tracing::debug!(
	target: LOG_TARGET,
	validation_code_hash = ?artifact_id.code_hash,
	worker_rip = idle_worker.is_none(),
	?result,
	"job finished.",
	);

At very minimal, make it a trace log.

ping @pepyakin