Work around a mypy bug

Author: A5rocks

src/trio/_subprocess.py

@@ -1122,13 +1122,26 @@ class UnixRunProcessMixin(TypedDict, total=False):
             check: bool
             deliver_cancel: Callable[[Process], Awaitable[None]] | None
 
+        # TODO: once https://github.com/python/mypy/issues/18692 is
+        #       fixed, move the `UnixRunProcessArgs` definition down.
         if sys.version_info >= (3, 11):
             UnixProcessArgs = UnixProcessArgs3_11
+
+            class UnixRunProcessArgs(UnixProcessArgs3_11, UnixRunProcessMixin):
+                """Arguments for run_process on Unix with 3.11+"""
+
         elif sys.version_info >= (3, 10):
             UnixProcessArgs = UnixProcessArgs3_10
+
+            class UnixRunProcessArgs(UnixProcessArgs3_10, UnixRunProcessMixin):
+                """Arguments for run_process on Unix with 3.10+"""
+
         else:
             UnixProcessArgs = UnixProcessArgs3_9
 
+            class UnixRunProcessArgs(UnixProcessArgs3_9, UnixRunProcessMixin):
+                """Arguments for run_process on Unix with 3.9+"""
+
         @overload  # type: ignore[no-overload-impl]
         async def open_process(
             command: StrOrBytesPath,
@@ -1147,9 +1160,6 @@ async def open_process(
             **kwargs: Unpack[UnixProcessArgs],
         ) -> trio.Process: ...
 
-        class UnixRunProcessArgs(UnixProcessArgs, UnixRunProcessMixin):
-            pass
-
         @overload  # type: ignore[no-overload-impl]
         async def run_process(
             command: StrOrBytesPath,