pipeline: targets-compositor: force variable BETA the same for all targets, reading from param/env passed to prepare/gha-matrix step

- this way it's consistent across all artifacts and images
- debs-to-repo-download: fix: use DEB_STORAGE instead of hardcoding output/debs (so BETA=yes works)

also:
- fix `Duplicate oci_target` message in mapper-oci-uptodate

lib/tools/info/mapper-oci-uptodate.py

@@ -150,7 +150,7 @@ for target in targets:
 
 	oci_target = target["out"]["artifact_full_oci_target"]
 	if oci_target in oci_target_map:
-		log.warning("Duplicate oci_target: {oci_target}")
+		log.warning(f"Duplicate oci_target: {oci_target}")
 		continue
 
 	oci_target_map[oci_target] = target

lib/tools/info/targets-compositor.py

@@ -109,6 +109,8 @@ for target_name in targets["targets"]:
 			one_invocation_vars = {}
 			one_invocation_vars.update(one_expansion["vars"])
 			one_invocation_vars.update(item)
+			# Special case for BETA, read this from TARGETS_BETA environment and force it.
+			one_invocation_vars.update({"BETA": os.environ.get("TARGETS_BETA", "")})
 			expanded = {"vars": one_invocation_vars, "configs": one_expansion["configs"], "pipeline": one_expansion["pipeline"]}
 			invocations_dict.append(expanded)