Fix finding DART on macOS

[scpeters]

🦟 Bug fix

Fixes cmake logic for finding DART for purposes of Physics System test.

Summary

There are some tests in the physics system that depend on the version of DART available on the system. In particular, Ubuntu 20.04 has DART 6.9.2, so any tests requiring features from 6.10 need to be disabled. This is accomplished by calling ign_find_package(DART) in test/integration/CMakeLists.txt and checking the available version.

This logic is now working properly on macOS, which has DART 6.12.1 from homebrew-core, but still does not run the tests that require 6.10:

• https://build.osrfoundation.org/view/ign-fortress/job/ignition_gazebo-ci-ign-gazebo6-homebrew-amd64/84/testReport/(root)/PhysicsSystemFixtureWithDart6_10/

165: [  SKIPPED ] PhysicsSystemFixtureWithDart6_10.JointPositionLimitsCommandComponent
165: [  SKIPPED ] PhysicsSystemFixtureWithDart6_10.JointVelocityLimitsCommandComponent
165: [  SKIPPED ] PhysicsSystemFixtureWithDart6_10.JointEffortLimitsCommandComponent
165/237 Test #165: INTEGRATION_physics_system .............................   Passed    8.87 sec

This pull request does the following:

• c8a463b: find DART without QUIET. It was failing to find DART the physics library and was using a FindDart cmake module for a different package, but QUIET was hiding that.
• 2e4eced: use CONFIG keyword to actually find DART correctly on macOS
• 9f8c3a2: fix a cmake warning that pops up

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.

[adityapande-1995]

Looks good, waiting for CI to run the DART 6.10 tests.

[scpeters]

Looks good, waiting for CI to run the DART 6.10 tests.

https://build.osrfoundation.org/job/ignition_gazebo-ci-pr_any-homebrew-amd64/8155/testReport/(root)/PhysicsSystemFixtureWithDart6_10/