bpo-44753: Don't use logfile extension when determining old files to be deleted (GH-27475) (GH-27487)

(cherry picked from commit 6ff890380971752299325bd28eab80ec936975cf)
diff --git a/Lib/logging/handlers.py b/Lib/logging/handlers.py
index 2a45f53..4cabc0d 100644
--- a/Lib/logging/handlers.py
+++ b/Lib/logging/handlers.py
@@ -359,7 +359,8 @@ def getFilesToDelete(self):
         dirName, baseName = os.path.split(self.baseFilename)
         fileNames = os.listdir(dirName)
         result = []
-        prefix = baseName + "."
+        # See bpo-44753: Don't use the extension when computing the prefix.
+        prefix = os.path.splitext(baseName)[0] + "."
         plen = len(prefix)
         for fileName in fileNames:
             if fileName[:plen] == prefix: