Enable show more files in diff for git <2.31 (#17733)

Unfortunately due to a misread on my behalf I missed that git diff only learned
--skip-to in version 2.31.0. Thus this functionality was not working on older versions
of git.

This PR adds a handler that simply allows for us to skip reading the diffs until
we find the correct file to skip to.

Fix #17731

Signed-off-by: Andrew Thornton <art27@cantab.net>

services/gitdiff/csv_test.go

@@ -188,7 +188,7 @@ c,d,e`,
 	}
 
 	for n, c := range cases {
-		diff, err := ParsePatch(setting.Git.MaxGitDiffLines, setting.Git.MaxGitDiffLineCharacters, setting.Git.MaxGitDiffFiles, strings.NewReader(c.diff))
+		diff, err := ParsePatch(setting.Git.MaxGitDiffLines, setting.Git.MaxGitDiffLineCharacters, setting.Git.MaxGitDiffFiles, strings.NewReader(c.diff), "")
 		if err != nil {
 			t.Errorf("ParsePatch failed: %s", err)
 		}