bpo-44011: Fix asyncio tests without ssl module (GH-25840)

Signed-off-by: Christian Heimes <christian@python.org>
diff --git a/Lib/asyncio/sslproto.py b/Lib/asyncio/sslproto.py
index e71875b..79734ab 100644
--- a/Lib/asyncio/sslproto.py
+++ b/Lib/asyncio/sslproto.py
@@ -12,7 +12,8 @@
 from . import transports
 from .log import logger
 
-SSLAgainErrors = (ssl.SSLWantReadError, ssl.SSLSyscallError)
+if ssl is not None:
+    SSLAgainErrors = (ssl.SSLWantReadError, ssl.SSLSyscallError)
 
 
 class SSLProtocolState(enum.Enum):