Npgsql: Drop support for Npgsql 7.x

`NpgsqlDataSourceBuilder` includes the `EnableDynamicJson` extension
starting with version 8.

Author: amotl

.github/workflows/lang-npgsql.yml

@@ -42,8 +42,8 @@ jobs:
       fail-fast: false
       matrix:
         os: [ 'ubuntu-22.04' ]
-        dotnet-version: [ '7.0.x', '8.0.x', '9.0.x' ]
-        npgsql-version: [ '7.0.9', '8.0.6', '9.0.2' ]
+        dotnet-version: [ '8.0.x', '9.0.x' ]
+        npgsql-version: [ '8.0.6', '9.0.2' ]
         cratedb-version: [ 'nightly' ]
 
     # https://docs.github.com/en/free-pro-team@latest/actions/guides/about-service-containers