ci: Test against Postgres 18

Signed-off-by: Corey <coreyearleon@icloud.com>

Author: cbaker6

.github/workflows/ci.yml

@@ -238,6 +238,9 @@ jobs:
           - name: PostgreSQL 17, PostGIS 3.5
             POSTGRES_IMAGE: postgis/postgis:17-3.5
             NODE_VERSION: 22.12.0
+          - name: PostgreSQL 18, PostGIS 3.6
+            POSTGRES_IMAGE: postgis/postgis:18-3.6
+            NODE_VERSION: 22.12.0
       fail-fast: false
     name: ${{ matrix.name }}
     timeout-minutes: 20