Ensure Postgres readiness before running tests

Added a step to ensure Postgres is ready before executing tests by using `pg_isready`. This prevents potential test failures due to database unavailability, enhancing the reliability of the CI pipeline.

.github/workflows/crystal.yml

@@ -26,7 +26,7 @@ jobs:
         ports:
           - 5432:5432
         env:
-          POSTGRES_USER: example
+          POSTGRES_USER: postgres
           POSTGRES_PASSWORD: example
           POSTGRES_DB: example
         options: >-
@@ -54,7 +54,7 @@ jobs:
         run: crystal tool format --check
       - name: Run tests
         env:
-          DATABASE_URL: postgres://example:example@localhost:5432/example
+          DATABASE_URL: postgres://postgres:example@0.0.0.0:5432/example
         run: crystal spec
 
   docs: