Remove deprecated PostgreSQL versions from build.yaml

Removed PostgreSQL versions 15 and 14 from the build configuration.

Author: gugu

.github/workflows/build.yaml

@@ -23,12 +23,6 @@ jobs:
             # renovate datasource=docker depName=ghcr.io/cloudnative-pg/postgresql
             cnpg_version: 16.4-7
             latest: "true"
-          - postgres_version: "15"
-            # renovate datasource=docker depName=ghcr.io/cloudnative-pg/postgresql
-            cnpg_version: 15.8-6
-          - postgres_version: "14"
-            # renovate datasource=docker depName=ghcr.io/cloudnative-pg/postgresql
-            cnpg_version: 14.13-6
     steps:
       - name: Checkout
         uses: actions/checkout@v4