RelNotes: fully spell negation

Signed-off-by: Carlo Marcelo Arenas Belón <carenas@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: carenas

Documentation/RelNotes/2.53.0.adoc

@@ -138,7 +138,7 @@ Fixes since v2.52
    (merge 42ed046866 jk/attr-macroexpand-wo-recursion later to maint).
 
  * Adding a repository that uses a different hash function is a no-no,
-   but "git submodule add" did nt prevent it, which has been corrected.
+   but "git submodule add" did not prevent it, which has been corrected.
    (merge 6fe288bfbc bc/submodule-force-same-hash later to maint).
 
  * An earlier check added to osx keychain credential helper to avoid