merge(third_party/git): Merge squashed git subtree at v2.23.0

Merge commit '1b593e1ea4' as 'third_party/git'

third_party/git/t/t5100/msg0014

@@ -0,0 +1,18 @@
+In real life, we will see a discussion that inspired this patch
+discussing related and unrelated things around >8 scissors mark
+in this part of the message.
+
+Subject: [PATCH] BLAH TWO
+
+And then we will see the scissors.
+
+ This line is not a scissors mark -- >8 -- but talks about it.
+ - - >8 - - please remove everything above this line - - >8 - -
+
+Subject: [PATCH] Teach mailinfo to ignore everything before -- >8 -- mark
+From: Junio C Hamano <gitster@pobox.com>
+
+This teaches mailinfo the scissors -- >8 -- mark; the command ignores
+everything before it in the message body.
+
+Signed-off-by: Junio C Hamano <gitster@pobox.com>