Fix docker_generate_datamodels.sh

The script `docker_generate_datamodels.sh` has been broken since we
started using virtual envs in the CI scripts a few weeks ago. Since
`build.sh` installs `zivid` in a venv, `generate_datamodels.sh` would
fail to find the package since it was not running in the same venv. This
commit fixes this by making `generate_datamodels.sh` activate the CI
venv set up by the previous steps. We only do this if there is no venv
currently activated, because we still want developers to be able to run
`generate_datamodels.sh` directly with their own venv.

continuous-integration/code-generation/generate_datamodels.sh

@@ -8,6 +8,11 @@
 SCRIPT_DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
 ROOT_DIR=$(realpath "$SCRIPT_DIR/../..")
 
+if [ -z "$VIRTUAL_ENV" ]; then
+    source $SCRIPT_DIR/../linux/venv.sh || exit $?
+    activate_venv || exit $?
+fi
+
 python3 -m pip install --requirement "$SCRIPT_DIR/../python-requirements/lint.txt" || exit $?
 
 python3 "$ROOT_DIR/continuous-integration/code-generation/datamodel_frontend_generator.py" \