treewide: Change URLs to HTTPS

Lots of URLs were HTTP redirect to HTTPS. Changed those and checked them
if there's actual content. Inspired by
https://github.com/NixOS/nixpkgs/issues/60004

pkgs/applications/version-management/git-and-tools/git2cl/default.nix

@@ -16,7 +16,7 @@ stdenv.mkDerivation {
   '';
 
   meta = {
-    homepage = http://josefsson.org/git2cl/;
+    homepage = https://savannah.nongnu.org/projects/git2cl;
     description = "Convert git logs to GNU style ChangeLog files";
     platforms = stdenv.lib.platforms.unix;
   };