Remove Python 3.7 branches (#11238)

stubs/gevent/gevent/os.pyi

@@ -26,6 +26,5 @@ if sys.platform != "win32":
         forkpty: Callable[[], tuple[int, int]] = ...,
     ) -> tuple[int, int]: ...
 
-    if sys.version_info >= (3, 8):
-        posix_spawn = os.posix_spawn
-        posix_spawnp = os.posix_spawnp
+    posix_spawn = os.posix_spawn
+    posix_spawnp = os.posix_spawnp