windows: fixed meta backup

[chenjie4255]

fix #5875

When a parent directory does not exist, the os package will return syscall.ENOTDIR on windows platform. see this link

test

Now can see a successful backup log.

C:\Users\....\Workspace\juicefs>juicefs.exe mount redis://192.168.31.134:6379/2 x: --backup-meta 5m
2025/03/27 16:39:07.964517 juicefs[21180] <INFO>: Meta address: redis://192.168.31.134:6379/2 [[email protected]:578]
2025/03/27 16:39:07.968331 juicefs[21180] <INFO>: Ping redis latency: 561.1µs [[email protected]:3653]
2025/03/27 16:39:07.976978 juicefs[21180] <INFO>: Data use minio://192.168.31.134:9000/jfscevol2/myjfs2/ [[email protected]:664]
2025/03/27 16:39:07.976978 juicefs[21180] <INFO>: JuiceFS version 1.3.0-dev+unknown [[email protected]:707]
2025/03/27 16:39:07.978488 juicefs[21180] <WARNING>: not enough space (8%) or inodes (100%) for caching in C:\Users\chenj\.juicefs\cache\d9206921-b56d-49d7-a0c6-0168d6e446a7\: free ratio should be >= 10% [newCacheStore@disk_cache.go:145]
2025/03/27 16:39:07.978488 juicefs[21180] <INFO>: Disk cache (C:\Users\chenj\.juicefs\cache\d9206921-b56d-49d7-a0c6-0168d6e446a7\): used ratio - [space 91.2%, inode 0%] [newCacheStore@disk_cache.go:147]
2025/03/27 16:39:08.031410 juicefs[21180] <INFO>: Create session 105 OK with version: 1.3.0-dev+unknown [[email protected]:519]
2025/03/27 16:39:08.040177 juicefs[21180] <INFO>: Prometheus metrics listening on 127.0.0.1:9567 [[email protected]:135]
The service juicefs has been started.
2025/03/27 16:39:38.442970 juicefs[21180] <WARNING>: Secret key is removed for the sake of safety [[email protected]:4026]
Dumped entries: 68/68 [==============================================================]  5241.5/s used: 12.9733ms
2025/03/27 16:39:38.504612 juicefs[21180] <INFO>: backup metadata succeed, fast mode: true, path: "minio://192.168.31.134:9000/jfscevol2/myjfs2/meta/dump-2025-03-27-083938.json.gz", used 64.9078ms [[email protected]:87]
2025/03/27 16:45:07.486145 juicefs[21180] <WARNING>: Secret key is removed for the sake of safety [[email protected]:4026]
Dumped entries: 68/68 [==============================================================]  6187.3/s used: 10.9903ms
2025/03/27 16:45:07.510320 juicefs[21180] <INFO>: backup metadata succeed, fast mode: true, path: "minio://192.168.31.134:9000/jfscevol2/myjfs2/meta/dump-2025-03-27-084507.json.gz", used 27.3595ms [[email protected]:87]