Fix senfile typo (#6265)

* Also in docs
diff --git a/Lib/asyncio/events.py b/Lib/asyncio/events.py
index fcca5d4..40946bb 100644
--- a/Lib/asyncio/events.py
+++ b/Lib/asyncio/events.py
@@ -24,7 +24,7 @@
 class SendfileNotAvailableError(RuntimeError):
     """Sendfile syscall is not available.
 
-    Raised if OS does not support senfile syscall for given socket or
+    Raised if OS does not support sendfile syscall for given socket or
     file type.
     """