Disable versioned_symbols test

[scpeters]

Nightly builds and a prerelease have been failing due to the INTEGRATION_versioned_symbols test failing since gazebosim/sdformat#1414 was merged forward to main / sdf15 in gazebosim/sdformat#1470. Strangely, the test only fails in these debbuilds. So just disable the test for now.

• https://build.osrfoundation.org/view/gz-ionic/job/sdformat15-debbuilder/518/

255: Test command: /usr/bin/bash "/home/jenkins/workspace/sdformat15-debbuilder/build/sdformat/obj-x86_64-linux-gnu/test/integration/all_symbols_have_version.bash" "/home/jenkins/workspace/sdformat15-debbuilder/build/sdformat/obj-x86_64-linux-gnu/lib/libsdformat15.so.15.0.0"
255: Working Directory: /home/jenkins/workspace/sdformat15-debbuilder/build/sdformat/obj-x86_64-linux-gnu/test/integration
255: Test timeout computed to be: 1500
255: ERROR: Found unversioned symbols:\n00000000017b6f90 N sdformat15_get_install_prefix_impl.cc.901ddfbe
Test #255: INTEGRATION_versioned_symbols ..........................***Failed    0.13 sec

[scpeters]

testing with this branch:

• https://build.osrfoundation.org/view/gz-ionic/job/sdformat15-debbuilder/526/

[scpeters]

proper fix was in gazebosim/sdformat#1474