Remove Bionic from future releases (Garden+)

[chapulina]

• See Garden support gazebo-tooling/release-tools#597

Summary

ign-gazebo7 will be on Garden.

Test it

No Bionic builds should be triggered.

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• 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 #1388 (4e8dfaf) into main (b9206e2) will decrease coverage by 0.69%.
The diff coverage is n/a.

❗ Current head 4e8dfaf differs from pull request most recent head 3f874cf. Consider uploading reports for the commit 3f874cf to get more accurate results

@@            Coverage Diff             @@
##             main    #1388      +/-   ##
==========================================
- Coverage   63.02%   62.33%   -0.70%     
==========================================
  Files         301      315      +14     
  Lines       24134    24252     +118     
==========================================
- Hits        15211    15117      -94     
- Misses       8923     9135     +212     

Impacted Files	Coverage Δ
...vator/vender/afsm/include/afsm/detail/observer.hpp	62.50% <0.00%> (-25.00%)	⬇️
src/systems/track_controller/TrackController.cc	46.38% <0.00%> (-24.56%)	⬇️
.../systems/elevator/vender/afsm/include/afsm/fsm.hpp	56.81% <0.00%> (-21.97%)	⬇️
src/systems/tracked_vehicle/TrackedVehicle.cc	46.22% <0.00%> (-18.56%)	⬇️
src/systems/physics/Physics.cc	66.04% <0.00%> (-5.81%)	⬇️
...or/vender/afsm/include/afsm/detail/base_states.hpp	96.36% <0.00%> (-3.64%)	⬇️
.../systems/triggered_publisher/TriggeredPublisher.cc	83.65% <0.00%> (-0.07%)	⬇️
src/SimulationRunner.cc	92.03% <0.00%> (-0.04%)	⬇️
src/systems/scene_broadcaster/SceneBroadcaster.cc	92.81% <0.00%> (-0.02%)	⬇️
src/EntityComponentManager.cc	88.37% <0.00%> (-0.02%)	⬇️
... and 55 more

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[chapulina]

This is good to go!

[chapulina]

CI is failing now because of geospatial, but it was passing one commit ago. I'll merge this to remove Bionic and #1262 will fix the rest.