Use the latest submodules when generating code is hooked

[Yang-33]

When we run generate-code.yml manually, this doesn't generated code when it's before line-openapi is not updated yet.
This change fixes it. Note line-bot-sdk-php and line-bot-sdk-nodejs do this. (python, java, and go don't do this yet)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (f1a675d) 55.19% compared to head (e6ca921) 55.19%.

❗ Current head e6ca921 differs from pull request most recent head e45bb1e. Consider uploading reports for the commit e45bb1e to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #419   +/-   ##
=======================================
  Coverage   55.19%   55.19%           
=======================================
  Files          87       87           
  Lines        5479     5479           
=======================================
  Hits         3024     3024           
  Misses       2233     2233           
  Partials      222      222           

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