fix: enforce venv activation in docker command

Author: seppzer0

builder/engines/generic_container.py

@@ -178,7 +178,7 @@ def build_image(self) -> str | None | CompletedProcess:
 
     @property
     def get_container_cmd(self) -> str:
-        return '{} run {} {} /bin/bash -c "{}"'.format(
+        return '{} run {} {} /bin/bash -c "source .venv/bin/activate && {}"'.format(
             self.benv,
             " ".join(self.container_options),
             self._name_image,