Add logging for worker spawn failures

[pepyakin]

No description provided.

[ordian]

Isn't the error logged here:

polkadot/node/core/pvf/src/prepare/pool.rs

Line 257 in a1399fb

tracing::warn!(target: LOG_TARGET, "failed to spawn a prepare worker: {:?}", err);

and

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

Line 300 in a1399fb

tracing::warn!(target: LOG_TARGET, "failed to spawn an execute worker: {:?}", err);

Or is it for test debugging?

[pepyakin]

It is logged there indeed. However, the error is just an opaque Bind or Accept without actually giving any hint for what've happened. Introduction nested data into these error variants that would give more information is an option, however, I figured that it is a bit weird to juggle this data around whereas we just want to print what is the error.