Fixed to use batch update

[kenkoooo]

No description provided.

[codecov-io]

Codecov Report

Merging #314 into master will decrease coverage by 2.21%.
The diff coverage is 57.14%.

@@            Coverage Diff             @@
##           master     #314      +/-   ##
==========================================
- Coverage    21.7%   19.49%   -2.22%     
==========================================
  Files          71       71              
  Lines        1963     1883      -80     
  Branches      286      267      -19     
==========================================
- Hits          426      367      -59     
+ Misses       1449     1446       -3     
+ Partials       88       70      -18

Impacted Files	Coverage Δ
...r-problems-backend/src/sql/problems_submissions.rs	66.66% <57.14%> (-6.37%)	⬇️

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