BUG: Fixed concat warning message (#21362)

(cherry picked from commit 649bfae)

Author: TomAugspurger

doc/source/whatsnew/v0.23.1.txt

@@ -107,7 +107,7 @@ Reshaping
 ^^^^^^^^^
 
 - Bug in :func:`concat` where error was raised in concatenating :class:`Series` with numpy scalar and tuple names (:issue:`21015`)
--
+- Bug in :func:`concat` warning message providing the wrong guidance for future behavior (:issue:`21101`)
 
 Other
 ^^^^^

pandas/core/indexes/api.py

@@ -24,9 +24,9 @@
 Sorting because non-concatenation axis is not aligned. A future version
 of pandas will change to not sort by default.
 
-To accept the future behavior, pass 'sort=True'.
+To accept the future behavior, pass 'sort=False'.
 
-To retain the current behavior and silence the warning, pass sort=False
+To retain the current behavior and silence the warning, pass 'sort=True'.
 """)