revert(3p/git): Revert merge of git upstream at v2.26.2

This causes cgit to serve error pages, which is undesirable.

This reverts commit 5229c9b232, reversing
changes made to f2b211131f.

third_party/git/contrib/diff-highlight/DiffHighlight.pm

@@ -72,7 +72,7 @@ sub handle_line {
 	      (?:$COLOR?\|$COLOR?[ ])* # zero or more trailing "|"
 	                         [ ]*  # trailing whitespace for merges
 	    /x) {
-		my $graph_prefix = $&;
+	        my $graph_prefix = $&;
 
 		# We must flush before setting graph indent, since the
 		# new commit may be indented differently from what we