Fix dll search paths for Ruby on Windows

[azeey]

🦟 Bug fix

Summary

The version of Ruby we use in our CI comes from https://rubyinstaller.org/, which according to their wiki says that the PATH environment variable is ignored when searching for dlls. This has been one of the reasons the gz tool doesn't work on Windows in our CI. This patch fixes it by setting RUBY_DLL_PATH equal to PATH.

Needed by gazebosim/sdformat#1374

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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)
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