Fix test worlds

[chapulina]

I uploaded new versions of the test worlds so that they now have both .world (deprecated) and .sdf files. And having a new world version made a bunch of tests fail.

It's unfortunate that the tests need to be updated whenever the worlds are changed, but the hope is that this isn't something we'll do very often 🤞

[codecov]

Codecov Report

Merging #100 into ign-fuel-tools3 will not change coverage.
The diff coverage is n/a.

@@               Coverage Diff                @@
##           ign-fuel-tools3     #100   +/-   ##
================================================
  Coverage            85.74%   85.74%           
================================================
  Files                   16       16           
  Lines                 2041     2041           
================================================
  Hits                  1750     1750           
  Misses                 291      291           

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[azeey]

Yeah, this is unfortunate. Same thing happened in #98. Maybe down the road we can add a function that returns the latest version directory.