Fix mint memory leak issue

[sanlee42]

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

What is the current behavior?

Issue Number: N/A

What is the new behavior?

Other information

[github-actions]

Benchmark for c1bf3f3

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Test	Base	PR	%
accumulator_append	578.2±10.41µs	579.9±10.16µs	+0.29%
block_apply/block_apply_10	263.4±0.68ms	263.7±0.59ms	+0.11%
block_apply/block_apply_1000	26.9±0.08s	26.9±0.04s	0.00%
get_with_proof/db_store	36.2±0.49µs	36.3±0.32µs	+0.28%
get_with_proof/mem_store	31.1±0.37µs	31.3±0.37µs	+0.64%
put_and_commit/db_store/1	95.7±4.69µs	95.1±4.60µs	-0.63%
put_and_commit/db_store/10	850.8±40.17µs	849.4±40.45µs	-0.16%
put_and_commit/db_store/100	7.4±0.33ms	7.3±0.33ms	-1.35%
put_and_commit/db_store/5	424.7±20.05µs	435.5±22.48µs	+2.54%
put_and_commit/db_store/50	3.8±0.17ms	3.8±0.18ms	0.00%
put_and_commit/mem_store/1	61.9±5.65µs	61.4±5.50µs	-0.81%
put_and_commit/mem_store/10	578.9±46.86µs	574.8±48.80µs	-0.71%
put_and_commit/mem_store/100	5.7±0.82ms	5.6±0.82ms	-1.75%
put_and_commit/mem_store/5	291.2±24.58µs	288.5±24.87µs	-0.93%
put_and_commit/mem_store/50	2.9±0.21ms	2.8±0.18ms	-3.45%
query_block/query_block_in(10)_times(100)	3.9±0.08ms	3.8±0.10ms	-2.56%
query_block/query_block_in(10)_times(1000)	39.2±1.18ms	38.2±2.40ms	-2.55%
query_block/query_block_in(10)_times(10000)	388.6±6.81ms	384.6±4.51ms	-1.03%
query_block/query_block_in(1000)_times(100)	944.3±8.08µs	938.6±6.21µs	-0.60%
query_block/query_block_in(1000)_times(1000)	9.4±0.07ms	9.4±0.07ms	0.00%
query_block/query_block_in(1000)_times(10000)	94.8±0.77ms	94.6±1.16ms	-0.21%
storage_transaction	1097.2±318.34µs	1076.8±291.30µs	-1.86%
vm/transaction_execution/1	311.6±1.15ms	310.5±2.00ms	-0.35%
vm/transaction_execution/10	98.4±0.21ms	97.8±0.18ms	-0.61%
vm/transaction_execution/20	92.1±0.79ms	91.5±0.55ms	-0.65%
vm/transaction_execution/5	120.1±0.47ms	119.7±1.18ms	-0.33%
vm/transaction_execution/50	106.1±0.32ms	105.7±0.36ms	-0.38%

[codecov]

Codecov Report

Merging #3351 (0d7f374) into master (0cab541) will decrease coverage by 0.19%.
The diff coverage is 12.50%.

@@            Coverage Diff             @@
##           master    #3351      +/-   ##
==========================================
- Coverage   32.15%   31.96%   -0.18%     
==========================================
  Files         500      500              
  Lines       46810    46814       +4     
  Branches    21299    21311      +12     
==========================================
- Hits        15045    14959      -86     
- Misses      17587    17637      +50     
- Partials    14178    14218      +40     

Flag	Coverage Δ
unittests	31.96% <12.50%> (-0.18%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
cmd/miner_client/src/job_client.rs	0.00% <0.00%> (ø)
cmd/miner_client/src/lib.rs	100.00% <ø> (ø)
cmd/miner_client/src/stratum_client.rs	0.00% <0.00%> (ø)
cmd/miner_client/src/stratum_client_service.rs	0.00% <ø> (ø)
cmd/miner_client/src/miner.rs	27.28% <11.12%> (-14.23%)	⬇️
cmd/miner_client/src/job_bus_client.rs	42.31% <14.29%> (-16.02%)	⬇️
miner/src/lib.rs	38.35% <100.00%> (-0.11%)	⬇️
executor/src/block_executor.rs	22.23% <0.00%> (-17.77%)	⬇️
consensus/src/dummy.rs	69.57% <0.00%> (-8.69%)	⬇️
... and 78 more

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