internal/rosa: helpers for common url formats

This cleans up call site of NewPackage.

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

internal/rosa/libpsl.go

@@ -7,10 +7,11 @@ func (t Toolchain) newLibpsl() (pkg.Artifact, string) {
 		version  = "0.21.5"
 		checksum = "XjfxSzh7peG2Vg4vJlL8z4JZJLcXqbuP6pLWkrGCmRxlnYUFTKNBqWGHCxEOlCad"
 	)
-	return t.NewPackage("libpsl", version, pkg.NewHTTPGetTar(
-		nil, "https://github.com/rockdaboot/libpsl/releases/download/"+
-			version+"/libpsl-"+version+".tar.gz",
-		mustDecode(checksum),
+	return t.NewPackage("libpsl", version, newFromGitHubRelease(
+		"rockdaboot/libpsl",
+		version,
+		"libpsl-"+version+".tar.gz",
+		checksum,
 		pkg.TarGzip,
 	), &PackageAttr{
 		Writable: true,