Call IDatabase::timestamp before inserting notification_read_timestamp
Call IDatabase::timestamp before inserting notification_read_timestamp

This is needed for proper cross-RDBMS support

This reapply a change from I46206e0b3a687dff3168a81cf0020e669133e876,
reverted with I1c8c409b7820512b3e31246a7f3d8c1cf4db209c.

Bug: T244898
Change-Id: I8b1387aff18d88088a993bc099165e9882658ac0

wikimedia/mediawiki-extensions-Echo,wikimedia/mediawiki-extensions-Echo,wikimedia/mediawiki-extensions-Echo,wikimedia/mediawiki-extensions-Echo