test: install polars in doctest session

Author: tswast

noxfile.py

@@ -108,7 +108,7 @@
 SYSTEM_TEST_EXTRAS_BY_PYTHON: Dict[str, List[str]] = {
     "3.9": ["tests"],
     "3.10": ["tests"],
-    "3.12": ["tests", "scikit-learn"],
+    LATEST_FULLY_SUPPORTED_PYTHON: ["all"],
     "3.13": ["tests"],
 }
 
@@ -427,8 +427,6 @@ def doctest(session: nox.sessions.Session):
             "third_party",
             "--ignore",
             "third_party/bigframes_vendored/ibis",
-            "--ignore",
-            "bigframes/core/compile/polars",
         ),
         test_folder="bigframes",
         check_cov=True,