Explicitly checkout a DB connection when creating a new thread for ST_GeomFromKML
Explicitly checkout a DB connection when creating a new thread for ST_GeomFromKML

As of Rails 5.1 database connections are shared between threads tests - this caused issues in `geom_from_kml`

`geom_from_kml` was unsuccessfully trying to create a new connection in a new thread. Instead it ended up
still on the main connection and hanging while it waited for other transactions to finish.

This caused permanent hangs in Rails test suites where use_transactional_fixtures=true

See https://github.com/rails/rails/pull/28083

culturecode/spatial_features