cli_TEST: Fix compatibility with CLI11 2.0

[traversaro]

🦟 Bug fix

Fixes compatibility with CLI11 2.0

Summary

If IGN_UTILS_VENDOR_CLI11 is set to OFF and CLI11 >= 2.0 was used, the compilation failed with:

2022-05-13T06:56:23.1223336Z [ 87%] Building CXX object cli/src/CMakeFiles/UNIT_cli_TEST.dir/cli_TEST.cc.o
2022-05-13T06:56:25.1811635Z /home/conda/feedstock_root/build_artifacts/libignition-utils1_1652424878233/work/cli/src/cli_TEST.cc: In function 'std::shared_ptr<TestOptions> addFlags(CLI::App&)':
2022-05-13T06:56:25.1816895Z /home/conda/feedstock_root/build_artifacts/libignition-utils1_1652424878233/work/cli/src/cli_TEST.cc:89:40: error: no matching function for call to 'CLI::App::add_option(const char [16], float&, const char [26], bool)'
2022-05-13T06:56:25.1817859Z    89 |       "Option with default value", true);
2022-05-13T06:56:25.1818289Z       |                                        ^
2022-05-13T06:56:25.1819571Z In file included from /home/conda/feedstock_root/build_artifacts/libignition-utils1_1652424878233

This is due to the the following change described in the changelog ( https://github.com/CLIUtils/CLI11/blob/main/CHANGELOG.md#version-20-simplification ):

The final "defaulted" bool has been removed, use ->capture_default_str() instead. Use app.option_defaults()->always_capture_default() to set this for all future options. CLIUtils/CLI11#597

Fortunatly, the suggested change works fine also with the vendored copy of CLI11, so we can just switch to that version to be future proof.

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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