internal/rosa: helpers for common url formats

This cleans up call site of NewPackage.

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

internal/rosa/cmake.go

@@ -13,10 +13,11 @@ func (t Toolchain) newCMake() (pkg.Artifact, string) {
 		version  = "4.3.1"
 		checksum = "RHpzZiM1kJ5bwLjo9CpXSeHJJg3hTtV9QxBYpQoYwKFtRh5YhGWpShrqZCSOzQN6"
 	)
-	return t.NewPackage("cmake", version, pkg.NewHTTPGetTar(
-		nil, "https://github.com/Kitware/CMake/releases/download/"+
-			"v"+version+"/cmake-"+version+".tar.gz",
-		mustDecode(checksum),
+	return t.NewPackage("cmake", version, newFromGitHubRelease(
+		"Kitware/CMake",
+		"v"+version,
+		"cmake-"+version+".tar.gz",
+		checksum,
 		pkg.TarGzip,
 	), &PackageAttr{
 		// test suite expects writable source tree