Reduce scheduler error-log noise for expected token validation events (SecurityTokenSignatureKeyNotFoundException)

CLIENT REQUEST

Since a few updates ago, we've been seeing recurring "SecurityTokenSignatureKeyNotFoundException" errors from the Devolutions Server scheduler roughly every 10 minutes, even though we don't experience any actual disconnections or malfunction.

It would help if this specific, apparently non-impactful event were logged at a lower severity (e.g., debug) instead of as an error, so it doesn't clutter the logs and cause unnecessary concern.