CI: Install petab for benchmark_model_petab when

... when using `--no-build-isolation`.

scripts/installAmiciSource.sh

@@ -33,7 +33,7 @@ fi
 export PYTHON_EXECUTABLE="${AMICI_PATH}/venv/bin/python"
 
 python -m pip install --upgrade pip wheel
-python -m pip install --upgrade pip setuptools cmake_build_extension==0.6.0 numpy
+python -m pip install --upgrade pip setuptools cmake_build_extension==0.6.0 numpy petab
 python -m pip install git+https://github.com/FFroehlich/pysb@fix_pattern_matching # pin to PR for SPM with compartments
 AMICI_BUILD_TEMP="${AMICI_PATH}/python/sdist/build/temp" \
   python -m pip install --verbose -e "${AMICI_PATH}/python/sdist[petab,test,vis]" --no-build-isolation