Fix tests in Key4hep@LCG stacks

[jmcarcell]

Summary

• recognize the LCG nightly stack and EL9 environment
• resolve local example modules consistently during fccanalysis run
• preload the matching build FastJet libraries for integration tests so ROOT cannot bind to Delphes' bundled FastJet symbols

Validation

• GCC 16.1.0 after source /cvmfs/sw-nightlies.hsf.org/key4hep/setup.sh --lcg
• workflow CMake options: WITH_ACTS=OFF, WITH_DD4HEP=ON, WITH_ONNX=ON, WITH_PODIO_DATASOURCE=ON
• ctest --output-on-failure — 52/52 passed

Merge order

Merge this PR only after #539 ("Fix compiler warnings"). (since otherwise the build will fail because of the warnings)

[jmcarcell]

@kjvbrt it would be probably good to have this and a tag if anyone is going to use FCCAnalyses in the release, as otherwise the same problems that we are finding in CI will be found there