internal/rosa: helpers for common url formats

This cleans up call site of NewPackage.

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

internal/rosa/libseccomp.go

@@ -7,10 +7,11 @@ func (t Toolchain) newLibseccomp() (pkg.Artifact, string) {
 		version  = "2.6.0"
 		checksum = "mMu-iR71guPjFbb31u-YexBaanKE_nYPjPux-vuBiPfS_0kbwJdfCGlkofaUm-EY"
 	)
-	return t.NewPackage("libseccomp", version, pkg.NewHTTPGetTar(
-		nil, "https://github.com/seccomp/libseccomp/releases/download/"+
-			"v"+version+"/libseccomp-"+version+".tar.gz",
-		mustDecode(checksum),
+	return t.NewPackage("libseccomp", version, newFromGitHubRelease(
+		"seccomp/libseccomp",
+		"v"+version,
+		"libseccomp-"+version+".tar.gz",
+		checksum,
 		pkg.TarGzip,
 	), &PackageAttr{
 		ScriptEarly: `