ci: Set PIP_ROOT_USER_ACTION=ignore

The Linux test job runs inside the Zephyr CI Docker image as root.

Signed-off-by: Stephanos Ioannidis <[email protected]>

Author: stephanosio

.github/workflows/ci.yml

@@ -1448,6 +1448,7 @@ jobs:
 
     env:
       SUBSET_COUNT: 3
+      PIP_ROOT_USER_ACTION: ignore
 
     steps:
     - name: Set up Python