feat: Add PostgreSQL support to CI test dependencies

- Add 'postgres' to testcontainers extras in test dependencies
- Add psycopg2-binary>=2.9.0 to test dependencies
- Enables PostgreSQL multi-backend tests to run in CI

This ensures CI will test both MySQL and PostgreSQL backends using
the test_multi_backend.py integration tests.

Author: dimitri-yatsenko

pyproject.toml

@@ -106,7 +106,8 @@ test = [
   "pytest-cov",
   "requests",
   "s3fs>=2023.1.0",
-  "testcontainers[mysql,minio]>=4.0",
+  "testcontainers[mysql,minio,postgres]>=4.0",
+  "psycopg2-binary>=2.9.0",
   "polars>=0.20.0",
   "pyarrow>=14.0.0",
 ]