include PATH in reserved var list

Author: ndeepak-baseten

truss/contexts/image_builder/serving_image_builder.py

@@ -103,7 +103,8 @@
 
 # PORT: knative reserved
 # HOSTNAME: set to the pod name by k8s
-K8S_RESERVED_ENVIRONMENT_VARIABLES = set(["PORT", "HOSTNAME"])
+# PATH: must be baked into the Dockerfile for $PATH expansion to work correctly
+K8S_RESERVED_ENVIRONMENT_VARIABLES = set(["PORT", "HOSTNAME", "PATH"])
 
 
 class RemoteCache(ABC):