chore: Add psycopg 2.9.10 into requirements-test.txt (#407)

psycopg 2.9.10 is supported on Python 3.13 for Windows now: psycopg/psycopg2#1736. So we can add psycopg 2.9.10 into requirements-test.txt.

This change does the following:
- Add psycopg2 into requirement-tests.txt.
- Fix the lint issue about enum member annotation: https://mypy.readthedocs.io/en/stable/changelog.html#change-to-enum-membership-semantics.
- Move test_psycopg2_direct_connection.py back into tests/system folder because it can now run since psycopg2 is in requirements-test.txt.

google/cloud/alloydb/connector/enums.py

@@ -22,9 +22,9 @@ class IPTypes(Enum):
     Enum for specifying IP type to connect to AlloyDB with.
     """
 
-    PUBLIC: str = "PUBLIC"
-    PRIVATE: str = "PRIVATE"
-    PSC: str = "PSC"
+    PUBLIC = "PUBLIC"
+    PRIVATE = "PRIVATE"
+    PSC = "PSC"
 
     @classmethod
     def _missing_(cls, value: object) -> None:
@@ -39,8 +39,8 @@ class RefreshStrategy(Enum):
     Enum for specifying refresh strategy to connect to AlloyDB with.
     """
 
-    LAZY: str = "LAZY"
-    BACKGROUND: str = "BACKGROUND"
+    LAZY = "LAZY"
+    BACKGROUND = "BACKGROUND"
 
     @classmethod
     def _missing_(cls, value: object) -> None:

requirements-test.txt

@@ -1,6 +1,15 @@
 asyncpg==0.30.0
 mock==5.1.0
 pg8000==1.31.2
+
+# psycopg 2.9.10 isn't supported on Python 3.9 for macos-latest GitHub runner.
+# It is supported for macos-12 runner:
+# https://github.com/psycopg/psycopg2/issues/1737. But macos-12 runner is
+# deprecated: https://github.com/actions/runner-images/issues/10721. So we
+# install psycopg 2.9.9 on Python 3.9 for macos-latest runner.
+psycopg2-binary==2.9.9; python_version == "3.9" and sys_platform == "darwin" 
+psycopg2-binary==2.9.10; python_version != "3.9" or sys_platform != "darwin"
+
 pytest==8.3.4
 pytest-asyncio==0.24.0
 pytest-cov==6.0.0