Update Postgres version (duffn#244)

Author: duffn

.github/workflows/test.yml

@@ -23,7 +23,7 @@ jobs:
           bundler-cache: true
       - uses: harmon758/postgresql-action@v1
         with:
-          postgresql version: 14
+          postgresql version: 15
           postgresql db: grape_boilerplate_test
           postgresql user: test
           postgresql password: password

postgres/Dockerfile

@@ -1,4 +1,3 @@
-# Current version in RDS
-FROM postgres:14
+FROM postgres:15
 
 COPY setup-db.sql /docker-entrypoint-initdb.d/