lib/fs: Check both old and new path when renaming (fixes #7426) (#7463)

lib/fs/casefs.go

@@ -224,6 +224,13 @@ func (f *caseFilesystem) Rename(oldpath, newpath string) error {
 	if err := f.checkCase(oldpath); err != nil {
 		return err
 	}
+	if err := f.checkCase(newpath); err != nil {
+		// Case-only rename is ok
+		e := &ErrCaseConflict{}
+		if !errors.As(err, &e) || e.Real != oldpath {
+			return err
+		}
+	}
 	if err := f.Filesystem.Rename(oldpath, newpath); err != nil {
 		return err
 	}