Param_TEST: Check return values of Param::Get/Set

[scpeters]

🦟 Bug fix

Adds more expectations to a unit test

Summary

While investigating how to implement a suggestion added in a comment in https://github.com/gazebosim/sdformat/commit/d3532946bc64fef713b30fbb1ab21a33603bf9dd, I noticed that the UNIT_Param_TEST has many calls to bool Param::Get and bool Param::Set without checking the return value. This adds expectations on the return value of those function calls, which will aid in addressing the aforementioned comment with a behavior change PR on main.

Checklist

• [X] 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)
• [X] codecheck passed (See contributing)
• [X] 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

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 92.42%. Comparing base (ff9b3ad) to head (e960bed). Report is 5 commits behind head on sdf14.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## sdf14 #1394 +/- ## ======================================= Coverage 92.42% 92.42% ======================================= Files 134 134 Lines 17751 17751 ======================================= Hits 16406 16406 Misses 1345 1345 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.