Add project() to examples

[chapulina]

🦟 Bug fix

Summary

This should fix CMake warnings that are turning the Jenkins build yellow since we migrated to Focal in gazebo-tooling/release-tools#565

Checklist

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

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[codecov]

Codecov Report

Merging #322 (e88b651) into ign-physics2 (042e2c3) will decrease coverage by 5.27%.
The diff coverage is n/a.

@@               Coverage Diff                @@
##           ign-physics2     #322      +/-   ##
================================================
- Coverage         82.84%   77.56%   -5.28%     
================================================
  Files               108      129      +21     
  Lines              4243     7114    +2871     
================================================
+ Hits               3515     5518    +2003     
- Misses              728     1596     +868     

Impacted Files	Coverage Δ
...nclude/ignition/physics/detail/RelativeQuantity.hh	95.36% <0.00%> (-4.64%)	⬇️
tpe/lib/src/Model.cc	95.41% <0.00%> (-2.97%)	⬇️
tpe/plugin/src/Base.hh	95.37% <0.00%> (-2.63%)	⬇️
dartsim/src/Base.hh	98.52% <0.00%> (-0.50%)	⬇️
tpe/lib/src/Shape.hh	100.00% <0.00%> (ø)
dartsim/src/plugin.cc	100.00% <0.00%> (ø)
dartsim/src/SimulationFeatures.hh	100.00% <0.00%> (ø)
include/ignition/physics/Geometry.hh	100.00% <0.00%> (ø)
include/ignition/physics/ForwardStep.hh	100.00% <0.00%> (ø)
include/ignition/physics/detail/Joint.hh	100.00% <0.00%> (ø)
... and 42 more

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