Disable Focal on Harmonic

[azeey]

Summary

Harmonic only supports Jammy so removing Focal CI.

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• 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 #2046 (a77a969) into main (d839caf) will increase coverage by 0.99%.
The diff coverage is 76.05%.

❗ Current head a77a969 differs from pull request most recent head 9292a2b. Consider uploading reports for the commit 9292a2b to get more accurate results

@@            Coverage Diff             @@
##             main    #2046      +/-   ##
==========================================
+ Coverage   64.48%   65.47%   +0.99%     
==========================================
  Files         341      312      -29     
  Lines       27143    29808    +2665     
==========================================
+ Hits        17502    19516    +2014     
- Misses       9641    10292     +651     

Files Changed	Coverage Δ
include/gz/sim/System.hh	100.00% <ø> (ø)
include/gz/sim/Util.hh	100.00% <ø> (ø)
include/gz/sim/components/Component.hh	100.00% <ø> (ø)
include/gz/sim/detail/EntityComponentManager.hh	94.01% <ø> (+0.14%)	⬆️
src/gui/plugins/modules/EntityContextMenu.cc	18.09% <0.00%> (-1.69%)	⬇️
src/gui/plugins/spawn/Spawn.cc	9.96% <0.00%> (-0.32%)	⬇️
.../gui/plugins/transform_control/TransformControl.cc	6.06% <0.00%> (-0.05%)	⬇️
...rc/systems/ackermann_steering/AckermannSteering.hh	100.00% <ø> (ø)
src/systems/joint_controller/JointController.hh	100.00% <ø> (ø)
...int_position_controller/JointPositionController.hh	100.00% <ø> (ø)
... and 43 more

... and 143 files with indirect coverage changes