stomp: Fix passing different types to std::min in cost_functions.hpp (backport #3244)

[mergify]

Description

std::min supports comparing scalar of the same type. Depending on the specific platform or compiler, values.cols() return type may not be compatible with long, so explicitly casting ensure that std::min compiles fine on any platform.

Specifically, I had encountered a compilation problem with this when compiling moveit with MSVC 2019.

Checklist

• Required by CI: Code is auto formatted using clang-format
• Extend the tutorials / documentation reference
• Document API changes relevant to the user in the MIGRATION.md notes
• Create tests, which fail without this PR reference
• Include a screenshot if changing a GUI
• While waiting for someone to review your request, please help review another open pull request to support the maintainers

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This is an automatic backport of pull request #3244 done by [Mergify](https://mergify.com).

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 44.55%. Comparing base (b1c45fd) to head (643190e).
Report is 1 commits behind head on jazzy.

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Additional details and impacted files

@@            Coverage Diff             @@
##            jazzy    #3245      +/-   ##
==========================================
+ Coverage   44.18%   44.55%   +0.38%     
==========================================
  Files         698      698              
  Lines       61587    61607      +20     
  Branches     7460     7461       +1     
==========================================
+ Hits        27205    27442     +237     
+ Misses      34215    33997     -218     
- Partials      167      168       +1     

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