[2.7] IDLE: Fix typo in keybindingDialog.py (GH-2322) (GH-12231)

Cherry picked by hand from a0e911b

Author: terryjreedy

Lib/idlelib/keybindingDialog.py

@@ -182,7 +182,7 @@ def ClearKeySeq(self):
 
     def LoadFinalKeyList(self):
         #these tuples are also available for use in validity checks
-        self.functionKeys=('F1','F2','F2','F4','F5','F6','F7','F8','F9',
+        self.functionKeys=('F1','F2','F3','F4','F5','F6','F7','F8','F9',
                 'F10','F11','F12')
         self.alphanumKeys=tuple(string.ascii_lowercase+string.digits)
         self.punctuationKeys=tuple('~!@#%^&*()_-+={}[]|;:,.<>/?')