ci: use shared postgres service for database tests

Replace spawning individual postgres clusters with a shared postgres
service container. This avoids the overhead of initdb and cluster
startup for each test session.

Changes:
- Add postgres:16 service to integration and check-downgrade jobs
- Switch TEST_DB_PROVIDER from 'postgres' to 'postgres-system'
- Add TEST_DB_PROVIDER_DSN environment variable for the service

Author: cdecker

.github/workflows/ci.yaml

@@ -249,6 +249,20 @@ jobs:
     runs-on: ubuntu-24.04
     needs:
       - compile
+    services:
+      postgres:
+        image: postgres:16
+        env:
+          POSTGRES_USER: postgres
+          POSTGRES_PASSWORD: postgres
+          POSTGRES_DB: postgres
+        ports:
+          - 5432:5432
+        options: >-
+          --health-cmd pg_isready
+          --health-interval 10s
+          --health-timeout 5s
+          --health-retries 5
     strategy:
       fail-fast: false
       matrix:
@@ -258,7 +272,7 @@ jobs:
             TEST_NETWORK: regtest
             VALGRIND: 1
           - CFG: compile-gcc
-            TEST_DB_PROVIDER: postgres
+            TEST_DB_PROVIDER: postgres-system
             TEST_NETWORK: regtest
           - CFG: compile-gcc
             TEST_DB_PROVIDER: sqlite3
@@ -315,6 +329,7 @@ jobs:
           PYTEST_PAR: 4
           TEST_DEBUG: 1
           TEST_DB_PROVIDER: ${{ matrix.TEST_DB_PROVIDER }}
+          TEST_DB_PROVIDER_DSN: postgres://postgres:postgres@localhost:5432/postgres
           TEST_NETWORK: ${{ matrix.TEST_NETWORK }}
           LIGHTNINGD_POSTGRES_NO_VACUUM: 1
           VALGRIND: ${{ matrix.VALGRIND }}
@@ -341,6 +356,20 @@ jobs:
       PYTEST_OPTS: -vvv --junit-xml=report.xml --timeout=1800 --durations=10
     needs:
       - compile
+    services:
+      postgres:
+        image: postgres:16
+        env:
+          POSTGRES_USER: postgres
+          POSTGRES_PASSWORD: postgres
+          POSTGRES_DB: postgres
+        ports:
+          - 5432:5432
+        options: >-
+          --health-cmd pg_isready
+          --health-interval 10s
+          --health-timeout 5s
+          --health-retries 5
     strategy:
       fail-fast: false
       matrix:
@@ -360,7 +389,7 @@ jobs:
           - NAME: postgres
             CFG: compile-gcc
             COMPILER: gcc
-            TEST_DB_PROVIDER: postgres
+            TEST_DB_PROVIDER: postgres-system
             TEST_NETWORK: regtest
           # And don't forget about elements (like cdecker did when
           # reworking the CI...)
@@ -433,6 +462,7 @@ jobs:
           PYTEST_PAR: 4
           TEST_DEBUG: 1
           TEST_DB_PROVIDER: ${{ matrix.TEST_DB_PROVIDER }}
+          TEST_DB_PROVIDER_DSN: postgres://postgres:postgres@localhost:5432/postgres
           TEST_NETWORK: ${{ matrix.TEST_NETWORK }}
           LIGHTNINGD_POSTGRES_NO_VACUUM: 1
         run: |