Enable gocritic equalFold and fix issues (#34952)

Continuation of https://github.com/go-gitea/gitea/pull/34678.

---------

Signed-off-by: silverwind <me@silverwind.io>

services/repository/files/file.go

@@ -144,7 +144,7 @@ func CleanGitTreePath(name string) string {
 	name = util.PathJoinRel(name)
 	// Git disallows any filenames to have a .git directory in them.
 	for part := range strings.SplitSeq(name, "/") {
-		if strings.ToLower(part) == ".git" {
+		if strings.EqualFold(part, ".git") {
 			return ""
 		}
 	}