internal/rosa: helpers for common url formats

This cleans up call site of NewPackage.

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

internal/rosa/squashfs.go

@@ -7,10 +7,11 @@ func (t Toolchain) newSquashfsTools() (pkg.Artifact, string) {
 		version  = "4.7.5"
 		checksum = "rF52wLQP-jeAmcD-48wqJcck8ZWRFwkax3T-7snaRf5EBnCQQh0YypMY9lwcivLz"
 	)
-	return t.NewPackage("squashfs-tools", version, pkg.NewHTTPGetTar(
-		nil, "https://github.com/plougher/squashfs-tools/releases/"+
-			"download/"+version+"/squashfs-tools-"+version+".tar.gz",
-		mustDecode(checksum),
+	return t.NewPackage("squashfs-tools", version, newFromGitHubRelease(
+		"plougher/squashfs-tools",
+		version,
+		"squashfs-tools-"+version+".tar.gz",
+		checksum,
 		pkg.TarGzip,
 	), &PackageAttr{
 		// uses source tree as scratch space