Rather than varying it, let's just use `postgis/postgis` everywhere.
This uses the latest version of PostGIS, in which some of the raster codes have changed. This seems benign (it's just one digit) in the hex stream. I can't find the relevant release notes though.
Also syncs _images.go_ and _databases.yaml_ so we use the same thing where possible.
PR-URL: https://github.com/hasura/graphql-engine-mono/pull/6903
GitOrigin-RevId: bb5c56f2e7ff69e4c008f1d658850af08c96badc