create: deal with EBUSY, fixes #8123

I put it into same class as EPERM and EACCES:
BackupPermissionError: borg is not permitted to access the file.

src/borg/archive.py

@@ -199,6 +199,7 @@ class BackupIO:
             E_MAP = {
                 errno.EPERM: BackupPermissionError,
                 errno.EACCES: BackupPermissionError,
+                errno.EBUSY: BackupPermissionError,
                 errno.ENOENT: BackupFileNotFoundError,
                 errno.EIO: BackupIOError,
             }