bpo-35128: Fix spacing issues in warning.warn() messages. (GH-10268)

diff --git a/Lib/ftplib.py b/Lib/ftplib.py
index 05840d4..9611282 100644
--- a/Lib/ftplib.py
+++ b/Lib/ftplib.py
@@ -732,7 +732,7 @@
                                  "exclusive")
             if keyfile is not None or certfile is not None:
                 import warnings
-                warnings.warn("keyfile and certfile are deprecated, use a"
+                warnings.warn("keyfile and certfile are deprecated, use a "
                               "custom context instead", DeprecationWarning, 2)
             self.keyfile = keyfile
             self.certfile = certfile