Fix MSVC "possible loss of data" warning

[azeey]

🦟 Bug fix

Summary

The warning appears in gz-launch and it's due to the fact that we're assigning a uint64_t to an int32_t.

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.19%. Comparing base (6ec4a1f) to head (2a328cc).

Additional details and impacted files

@@            Coverage Diff             @@
##           gz-msgs10     #434   +/-   ##
==========================================
  Coverage      98.19%   98.19%           
==========================================
  Files             27       27           
  Lines           1166     1166           
==========================================
  Hits            1145     1145           
  Misses            21       21           

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