[Fix] Update resource limit

[Junjun2016]

The limited resource adjustment will reduce the base file-open soft limit to 4096. Sometimes it will result in 'OSError: [Error 24] Too many open files' during training process when large file-open needed (>4096).

[codecov]

Codecov Report

Merging #700 (a1677eb) into master (f5be6e2) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head a1677eb differs from pull request most recent head 6ff38d9. Consider uploading reports for the commit 6ff38d9 to get more accurate results

@@           Coverage Diff           @@
##           master     #700   +/-   ##
=======================================
  Coverage   85.18%   85.18%           
=======================================
  Files         105      105           
  Lines        5670     5671    +1     
  Branches      923      923           
=======================================
+ Hits         4830     4831    +1     
  Misses        662      662           
  Partials      178      178           

Flag	Coverage Δ
unittests	85.17% <100.00%> (+<0.01%)	⬆️

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Impacted Files	Coverage Δ
mmseg/datasets/builder.py	89.47% <100.00%> (+0.14%)	⬆️

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