github: create group and home for test-user

The cloud images of opensuse have changed a little and now the neither the group
nor home is created by default when using useradd.

Signed-off-by: Maciej Borzecki <maciej.borzecki@canonical.com>

.github/workflows/test.yaml

@@ -549,7 +549,7 @@ jobs:
         esac
     - name: Set up test user
       run: |
-        useradd test-user
+        useradd -U -m test-user
         chown -R test-user:test-user $PWD
 
     - name: Unit tests (Go)