internal/rosa: helpers for common url formats

This cleans up call site of NewPackage.

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

internal/rosa/fakeroot.go

@@ -7,11 +7,11 @@ func (t Toolchain) newFakeroot() (pkg.Artifact, string) {
 		version  = "1.37.2"
 		checksum = "4ve-eDqVspzQ6VWDhPS0NjW3aSenBJcPAJq_BFT7OOFgUdrQzoTBxZWipDAGWxF8"
 	)
-	return t.NewPackage("fakeroot", version, pkg.NewHTTPGetTar(
-		nil, "https://salsa.debian.org/clint/fakeroot/-/archive/upstream/"+
-			version+"/fakeroot-upstream-"+version+".tar.bz2",
-		mustDecode(checksum),
-		pkg.TarBzip2,
+	return t.NewPackage("fakeroot", version, newFromGitLab(
+		"salsa.debian.org",
+		"clint/fakeroot",
+		"upstream/"+version,
+		checksum,
 	), &PackageAttr{
 		Patches: []KV{
 			{"remove-broken-docs", `diff --git a/doc/Makefile.am b/doc/Makefile.am