localtest: Fix regression after package filtering improvements

Commit a27543ba "gitlab-ci: Extend filtering by package to all
retrieval jobs" broke `localtest` since `PROJECTS_NAMESPACE` was not set
and no GitLab project could be properly retrieved.

Signed-off-by: Emanuele Aina <emanuele.aina@collabora.com>

localtest

@@ -42,6 +42,7 @@ if __name__ == "__main__":
 
     print("set -eux")
     print(f"FILTER_PACKAGES={args.filter_packages or '*'}")
+    print("PROJECTS_NAMESPACE=pkg")
     print("ARTIFACT_URL=none")
     print("TRIGGER_UPDATES=")
     print("TRIGGER_FROM_JOB=")