test: skip ibis test on unsupported python version (vega#3486)

* test: skip `ibis` test on unsupported `python` version

Always was emitting the same warning on `3.8`, `3.9`:

```
================================================================================================= warnings summary =================================================================================================  tests/vegalite/v5/test_api.py::test_ibis_with_date_32   /altair/altair/vegalite/v5/api.py:233: UserWarning: data of type <class 'ibis.expr.types.relations.Table'> not recognized     warnings.warn(f"data of type {type(data)} not recognized", stacklevel=1)  -- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html ==================================================================================== 210 passed, 1 xfailed, 1 warning in 17.92s ====================================================================================
```

* test: lower the minimum `python` 3.10 -> 3.9 for `ibis`

vega#3486 (comment)

tests/vegalite/v5/test_api.py

@@ -1526,6 +1526,11 @@ def test_polars_with_pandas_nor_pyarrow(monkeypatch: pytest.MonkeyPatch):
     assert "numpy" not in sys.modules
 
 
+@pytest.mark.skipif(
+    sys.version_info < (3, 9),
+    reason="The maximum `ibis` version installable on Python 3.8 is `ibis==5.1.0`,"
+    " which doesn't support the dataframe interchange protocol.",
+)
 @pytest.mark.skipif(
     Version("1.5") > PANDAS_VERSION,
     reason="A warning is thrown on old pandas versions",