internal/rosa: helpers for common url formats

This cleans up call site of NewPackage.

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

internal/rosa/pcre2.go

@@ -9,10 +9,11 @@ func (t Toolchain) newPCRE2() (pkg.Artifact, string) {
 		version  = "10.47"
 		checksum = "IbC24vVayju6nB9EhrBPSDexk22wDecdpyrjgC3nCZXkwTnUjq4CD2q5sopqu6CW"
 	)
-	return t.NewPackage("pcre2", version, pkg.NewHTTPGetTar(
-		nil, "https://github.com/PCRE2Project/pcre2/releases/download/"+
-			"pcre2-"+version+"/pcre2-"+version+".tar.bz2",
-		mustDecode(checksum),
+	return t.NewPackage("pcre2", version, newFromGitHubRelease(
+		"PCRE2Project/pcre2",
+		"pcre2-"+version,
+		"pcre2-"+version+".tar.bz2",
+		checksum,
 		pkg.TarBzip2,
 	), &PackageAttr{
 		ScriptEarly: `