Akonadi::SpecialCollectionsRequestJob: increase timeout from 10s to 30s

When KMail is started as part of session restoration, many things are
happening at the same time, and it can happen that another program has
the lock for more than 10 seconds.

This reduces the risk of being greeted in the morning by a suicide note:
"The EMail program encountered a fatal error and will terminate now.
The error was: Timeout trying to get lock"

BUG: 246027
REVIEW: 127175