[Dev] Use isawaitable over iscoroutine for [p]debug (#2202)

Allows for non-coroutine awaitables (such as config's `_ValueCtxManager`) to be awaited from debug.

Signed-off-by: Toby Harradine <tobyharradine@gmail.com>

redbot/core/dev_commands.py

@@ -116,7 +116,7 @@ class Dev(commands.Cog):
             await ctx.send(box("{}: {!s}".format(type(e).__name__, e), lang="py"))
             return
 
-        if asyncio.iscoroutine(result):
+        if inspect.isawaitable(result):
             result = await result
 
         self._last_result = result