Install sdf/1.8 to versioned path

[scpeters]

🦟 Bug fix

Fixes a mistake from merging forward in #808.

Summary

The SDF_MAJOR_VERSION variables were all replaced with PROJECT_VERSION_MAJOR in #780, but when merging forward in #808, this replacement was forgotten in the sdf/1.8 folder, which did not exist in the sdf10 branch. This causes conflicts between the sdfomat-X packages on Ubuntu.

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.

[codecov-commenter]

Codecov Report

Merging #890 (2382182) into sdf11 (b0647c9) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##            sdf11     #890   +/-   ##
=======================================
  Coverage   88.91%   88.91%           
=======================================
  Files          73       73           
  Lines       11094    11094           
=======================================
  Hits         9864     9864           
  Misses       1230     1230           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update b0647c9...2382182. Read the comment docs.

[azeey]

Looks good. I wonder if we should alias SDF_MAJOR_VERSION to PROJECT_VERSION_MAJOR?

[scpeters]

Looks good. I wonder if we should alias SDF_MAJOR_VERSION to PROJECT_VERSION_MAJOR?

we still have it in the C++ API, but I thought we had eliminated all instances of it. I was wrong of course, but I don't see any more instances of it now, having checked again on these future branches

[osrf-triage]

This pull request has been mentioned on Gazebo Community. There might be relevant details there:

https://community.gazebosim.org/t/new-ignition-releases-2022-03-25-fortress-edifice-citadel/1343/1

[osrf-triage]

This pull request has been mentioned on Gazebo Community. There might be relevant details there:

https://community.gazebosim.org/t/new-ignition-releases-2022-04-13-fortress-edifice/1367/1