Webhook requests can take 20+ seconds. During that time we hold
on to a database connection. With this commit, the Webhook transport
closes its DB connection before making a curl call.
With psycopg2 this does not have much effect. But with
psycopg 3 & connection pooling we will be able to use more
sendalerts workers than we have database connections. While one
worker is busy making a slow curl call, another worker can
grab its freed up connection and do some work.
Django's test runner is not happy with connections closed
mid-test, so I patched out close_old_connections() in affected tests.
a463daa775