Do not update StoreEntry expiration after errorAppendEntry() (#1580)

Do not update StoreEntry expiration after errorAppendEntry() (#1580)

errorAppendEntry() is responsible for setting entry expiration times,
which it does by calling StoreEntry::storeErrorResponse() that calls
StoreEntry::negativeCache().

This change was triggered by a vulnerability report by Joshua Rogers at
https://megamansec.github.io/Squid-Security-Audit/cache-uaf.html where
it was filed as "Use-After-Free in Cache Manager Errors". The reported
"use after free" vulnerability was unknowingly addressed by 2022 commit
1fa761a that removed excessively long "reentrant" store_client calls
responsible for the disappearance of the properly locked StoreEntry in
this (and probably other) contexts.