internal/rosa: helpers for common url formats

This cleans up call site of NewPackage.

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

internal/rosa/libexpat.go

@@ -11,11 +11,11 @@ func (t Toolchain) newLibexpat() (pkg.Artifact, string) {
 		version  = "2.7.5"
 		checksum = "vTRUjjg-qbHSXUBYKXgzVHkUO7UNyuhrkSYrE7ikApQm0g-OvQ8tspw4w55M-1Tp"
 	)
-	return t.NewPackage("libexpat", version, pkg.NewHTTPGetTar(
-		nil, "https://github.com/libexpat/libexpat/releases/download/"+
-			"R_"+strings.ReplaceAll(version, ".", "_")+"/"+
-			"expat-"+version+".tar.bz2",
-		mustDecode(checksum),
+	return t.NewPackage("libexpat", version, newFromGitHubRelease(
+		"libexpat/libexpat",
+		"R_"+strings.ReplaceAll(version, ".", "_"),
+		"expat-"+version+".tar.bz2",
+		checksum,
 		pkg.TarBzip2,
 	), nil, (*MakeHelper)(nil),
 		Bash,