Relax expectations about zero in SpeedLimiter_TEST to make ARM happy

[j-rivero]

🦟 Bug fix

Fixes compilation on some ARM builds

Summary

Some ARM packaging jobs are failing with problems on the precision of zero in test under SpeedLimiter:

[ RUN      ] SpeedLimiterTest.Default
/var/lib/jenkins/workspace/ign-math6-debbuilder/build/ignition-math-6.8.0/src/SpeedLimiter_TEST.cc:60: Failure
Expected equality of these values:
  0.0
    Which is: 0
  limiter.Limit(vel, 4.0, 3.0, 1ms)
    Which is: -8.3266726846886741e-17
[  FAILED  ] SpeedLimiterTest.Default (6 ms)

With this patch the build compiles: https://build.osrfoundation.org/job/ign-math6-debbuilder/734/

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)

Note to maintainers: Remember to use Squash-Merge

[codecov]

Codecov Report

Merging #204 (739fb63) into ign-math6 (6b5c704) will not change coverage.
The diff coverage is n/a.

❗ Current head 739fb63 differs from pull request most recent head 564f031. Consider uploading reports for the commit 564f031 to get more accurate results

@@            Coverage Diff             @@
##           ign-math6     #204   +/-   ##
==========================================
  Coverage      99.21%   99.21%           
==========================================
  Files             65       65           
  Lines           6087     6087           
==========================================
  Hits            6039     6039           
  Misses            48       48           

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