leave pypy-3.10 for a different PR, re-fix tuple->Tuple mypy fail on 3.8

Author: jakkdl

.github/workflows/ci.yml

@@ -92,7 +92,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python: ['pypy-3.9', 'pypy-3.10', '3.8', '3.9', '3.10', '3.11', '3.12-dev', 'pypy-3.9-nightly', 'pypy-3.10-nightly']
+        python: ['pypy-3.9', '3.8', '3.9', '3.10', '3.11', '3.12-dev', 'pypy-3.9-nightly']
         check_formatting: ['0']
         extra_name: ['']
         include:

trio/_channel.py

@@ -99,7 +99,7 @@ def _open_memory_channel(
 if TYPE_CHECKING:
     # written as a class so you can say open_memory_channel[int](5)
     # Need to use Tuple instead of tuple due to CI check running on 3.8
-    class open_memory_channel(tuple[MemorySendChannel[T], MemoryReceiveChannel[T]]):
+    class open_memory_channel(Tuple[MemorySendChannel[T], MemoryReceiveChannel[T]]):
         def __new__(  # type: ignore[misc]  # "must return a subtype"
             cls, max_buffer_size: int
         ) -> tuple[MemorySendChannel[T], MemoryReceiveChannel[T]]: