internal/rosa: helpers for common url formats

This cleans up call site of NewPackage.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/rosa/etc.go

@@ -135,10 +135,11 @@ func newIANAEtc() pkg.Artifact {
 		version  = "20251215"
 		checksum = "kvKz0gW_rGG5QaNK9ZWmWu1IEgYAdmhj_wR7DYrh3axDfIql_clGRHmelP7525NJ"
 	)
-	return pkg.NewHTTPGetTar(
-		nil, "https://github.com/Mic92/iana-etc/releases/download/"+
-			version+"/iana-etc-"+version+".tar.gz",
-		mustDecode(checksum),
+	return newFromGitHubRelease(
+		"Mic92/iana-etc",
+		version,
+		"iana-etc-"+version+".tar.gz",
+		checksum,
 		pkg.TarGzip,
 	)
 }