try Protocol38 on EagerSeriesNamespace only

- Regular `Protocol` failed on `3.8`, `3.9`, `3.10`
  - (f4c0cd6)
- Testing if I need on **every** protocol, or just the one with an `__init__`

Author: dangotbanned

narwhals/_compliant/series.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import sys
 from typing import TYPE_CHECKING
 from typing import Any
 from typing import Iterable
@@ -21,6 +22,16 @@
 from narwhals.utils import _SeriesNamespace
 from narwhals.utils import unstable
 
+if not TYPE_CHECKING:  # pragma: no cover
+    if sys.version_info >= (3, 9):
+        from typing import Protocol as Protocol38
+    else:
+        from typing import Generic as Protocol38
+else:  # pragma: no cover
+    # TODO @dangotbanned: Remove after dropping `3.8` (#2084)
+    # - https://github.com/narwhals-dev/narwhals/pull/2064#discussion_r1965921386
+    from typing import Protocol as Protocol38
+
 if TYPE_CHECKING:
     from types import ModuleType
 
@@ -306,7 +317,7 @@ def struct(self) -> Any: ...
 
 class EagerSeriesNamespace(  # type: ignore[misc]
     _SeriesNamespace[EagerSeriesT_co, NativeSeriesT_co],
-    Protocol[EagerSeriesT_co, NativeSeriesT_co],
+    Protocol38[EagerSeriesT_co, NativeSeriesT_co],
 ):
     _compliant_series: EagerSeriesT_co