Some minor changes to hydrodynamic flags test

[arjo129]

🦟 Bug fix

This commit changes the url to use the more recent url. It also removes the scene-broadcaster plugin as we don't need it in the test itself.

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)
• 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]

Codecov Report

Merging #1772 (404f9c7) into ign-gazebo6 (77ea80c) will not change coverage.
The diff coverage is n/a.

❗ Current head 404f9c7 differs from pull request most recent head db8b436. Consider uploading reports for the commit db8b436 to get more accurate results

@@             Coverage Diff              @@
##           ign-gazebo6    #1772   +/-   ##
============================================
  Coverage        64.65%   64.65%           
============================================
  Files              321      321           
  Lines            26275    26275           
============================================
  Hits             16987    16987           
  Misses            9288     9288           

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[mjcarroll]

Can I get a sign-off here? Thanks!

[arjo129]

Whoops. Apologies, I've signed off now.