Fix: Unlock locked object on its lock removal

[carpawell]

See #1227 (comment).

Also, more tests in SE will be added if PR is valid after the discussion.

[codecov]

Codecov Report

Merging #1440 (2b24044) into master (cc6209e) will increase coverage by 0.01%.
The diff coverage is 15.49%.

❗ Current head 2b24044 differs from pull request most recent head f97bf54. Consider uploading reports for the commit f97bf54 to get more accurate results

@@            Coverage Diff             @@
##           master    #1440      +/-   ##
==========================================
+ Coverage   36.52%   36.53%   +0.01%     
==========================================
  Files         305      305              
  Lines       18001    18065      +64     
==========================================
+ Hits         6574     6600      +26     
- Misses      10861    10896      +35     
- Partials      566      569       +3     

Impacted Files	Coverage Δ
pkg/core/object/fmt.go	58.55% <0.00%> (-2.00%)	⬇️
pkg/local_object_storage/engine/delete.go	0.00% <0.00%> (ø)
pkg/local_object_storage/engine/inhume.go	64.51% <0.00%> (+6.18%)	⬆️
pkg/local_object_storage/shard/gc.go	22.38% <0.00%> (-1.18%)	⬇️
pkg/local_object_storage/shard/shard.go	60.71% <0.00%> (-2.25%)	⬇️
pkg/local_object_storage/shard/inhume.go	37.83% <10.00%> (-12.17%)	⬇️
pkg/local_object_storage/metabase/inhume.go	72.63% <30.43%> (-11.58%)	⬇️
pkg/local_object_storage/engine/shards.go	79.72% <100.00%> (+0.27%)	⬆️
pkg/local_object_storage/metabase/util.go	94.82% <100.00%> (+0.18%)	⬆️
pkg/local_object_storage/metabase/lock.go	63.29% <0.00%> (+8.86%)	⬆️
... and 1 more

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[carpawell]

Would be added to master via the feature branch: #1461.