fixed duplicate attachments on dump on windows (go-gitea#28019)

Hi,

This PR fixes go-gitea#27988. The use of `path.join`(which uses `/` as the file
separator) to construct paths and comparing them with paths constructed
using `filepath.join`(which uses platform specific file separator) is
the root cause of this issue.

The desired behavior is to ignore attachments when dumping data
directory. Due to the what's mentioned above, the function
`addRecursiveExclude` is not actually ignoring the attachments directory
and is being written to the archive. The attachment directory is again
added to the archive (with different file separator as mentioned in the
issue) causing a duplicate entry on windows.

The solution is to use `filepath.join` in `addResursiveExclude` to
construct `currentAbsPath`.

cmd/dump.go

@@ -452,7 +452,7 @@ func addRecursiveExclude(w archiver.Writer, insidePath, absPath string, excludeA
 		return err
 	}
 	for _, file := range files {
-		currentAbsPath := path.Join(absPath, file.Name())
+		currentAbsPath := filepath.Join(absPath, file.Name())
 		currentInsidePath := path.Join(insidePath, file.Name())
 		if file.IsDir() {
 			if !util.SliceContainsString(excludeAbsPath, currentAbsPath) {