Fix senfile typo (GH-6265) (#6274)

* Also in docs
(cherry picked from commit 65a34709f60711f7c46031d4c6c420f567bc790a)

Co-authored-by: Sam Dunster <me@sdunster.com>
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.
     """