Only import basemodelica if needed

[AnHeuermann]

Issue

The Jenkins default jobs (without Julia) are failing because of

$ stdbuf -oL -eL time ./test.py --ompython_omhome=/usr --extraflags= --extrasimflags= --branch=master --output=libraries.openmodelica.org:/var/www/libraries.openmodelica.org/branches/master/ --libraries=/home/hudson/saved_omc/libraries/.openmodelica/libraries/ --jobs=0 configs/conf.json
    Updating registry at `~/.julia/registries/General.toml`
   Resolving package versions...
ERROR: Unsatisfiable requirements detected for package OpenSSL_jll [458c3c95]:
 OpenSSL_jll [458c3c95] log:
 ├─possible versions are: 3.5.4 or uninstalled
 └─restricted to versions 3.0 by project [4facbee2] — no versions left
   └─project [4facbee2] log:
     ├─possible versions are: 0.0.0 or uninstalled
     └─project [4facbee2] is fixed to version 0.0.0

https://test.openmodelica.org/jenkins/blue/organizations/jenkins/LibraryTesting%2FLibraryTest/detail/LibraryTest/10566/pipeline

Changes

• Only import Python package juliacall if really needed.

[casella]

@AnHeuermann, is it "Only import basemodelica if needed" or Only import juliacall if needed"?