Documentation/RelNotes: fix a typo in 2.28's relnotes

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/RelNotes/2.28.0.txt

diff --git a/Documentation/RelNotes/2.28.0.txt b/Documentation/RelNotes/2.28.0.txt
index 5f1413a..6baf781 100644
--- a/Documentation/RelNotes/2.28.0.txt
+++ b/Documentation/RelNotes/2.28.0.txt
@@ -116,7 +116,7 @@
    configuration variables in extensions.* namespace were supposed to
    have special meaning in repositories whose version numbers are 1 or
    higher), but this was a bit too big a change.  The behaviour in
-   recent versions of Git where certaion extensions.* were honored by
+   recent versions of Git where certain extensions.* were honored by
    mistake even in version 0 repositories has been restored.