internal/rosa: helpers for common url formats

This cleans up call site of NewPackage.

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

internal/rosa/git.go

@@ -12,10 +12,10 @@ func (t Toolchain) newGit() (pkg.Artifact, string) {
 		version  = "2.53.0"
 		checksum = "rlqSTeNgSeVKJA7nvzGqddFH8q3eFEPB4qRZft-4zth8wTHnbTbm7J90kp_obHGm"
 	)
-	return t.NewPackage("git", version, pkg.NewHTTPGetTar(
-		nil, "https://www.kernel.org/pub/software/scm/git/"+
+	return t.NewPackage("git", version, newTar(
+		"https://www.kernel.org/pub/software/scm/git/"+
 			"git-"+version+".tar.gz",
-		mustDecode(checksum),
+		checksum,
 		pkg.TarGzip,
 	), &PackageAttr{
 		ScriptEarly: `