fix MultipartUpload test

[zhijian-pro]

For UFile: The size of all parts except the last part cannot be less than 4MB, otherwise calling the FinishMultipartUpload API will fail.

ref #3272

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.04 🎉

Comparison is base (caefb53) 55.61% compared to head (6cb31e5) 55.66%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3298      +/-   ##
==========================================
+ Coverage   55.61%   55.66%   +0.04%     
==========================================
  Files         142      142              
  Lines       33825    33825              
==========================================
+ Hits        18812    18828      +16     
+ Misses      13019    13006      -13     
+ Partials     1994     1991       -3     

Impacted Files	Coverage Δ
cmd/sync.go	50.34% <100.00%> (ø)
pkg/meta/redis.go	66.75% <0.00%> (+0.03%)	⬆️
pkg/chunk/cached_store.go	73.10% <0.00%> (+0.14%)	⬆️
pkg/chunk/disk_cache.go	73.54% <0.00%> (+0.29%)	⬆️
pkg/vfs/reader.go	79.90% <0.00%> (+0.63%)	⬆️
pkg/vfs/handle.go	84.32% <0.00%> (+0.74%)	⬆️
pkg/vfs/writer.go	78.65% <0.00%> (+1.16%)	⬆️
pkg/fuse/context.go	73.17% <0.00%> (+7.31%)	⬆️

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[github-actions]

Mutate Test Report
pkg/object/object_storage_test.go-1-1: score:0.17 failed:10, passed:2, compile error:1, out of coverage:0, skip by comment:0, others:0
Job detail: https://github.com/juicedata/juicefs/actions/runs/4350643566/jobs/7605744671

Usage: https://github.com/juicedata/juicefs/blob/main/.github/scripts/mutate/how_to_use_mutate_test.md

[davies]

Can we make sure that sync use correct part size for UFile?

[davies]

use MinPartSize