chore(ci): share database hostname and auth

.drone.yml

@@ -40,9 +40,9 @@ steps:
     image: 'hexpm/elixir:1.16.2-erlang-26.2.5-debian-bookworm-20240513-slim'
     environment:
       MIX_ENV: test
-      POSTGRES_HOST: db
-      POSTGRES_USER: postgres
-      POSTGRES_PASS: postgres
+      POSTGRES_HOST: &db_host db
+      POSTGRES_USER: &db_user postgres
+      POSTGRES_PASS: &db_pass postgres
     commands:
       - mix do local.rebar --force, local.hex --force, deps.get, deps.compile
       - mix compile
@@ -69,11 +69,11 @@ steps:
       region: us-east-1
 
 services:
-  - name: db
+  - name: *db_host
     image: *postgres
     environment:
-      POSTGRES_USER: postgres
-      POSTGRES_PASSWORD: postgres
+      POSTGRES_USER: *db_user
+      POSTGRES_PASSWORD: *db_pass
 
 ---
 kind: pipeline