ci: Use GitHub Actions for CI/CD

nix/overlays/default.nix

@@ -1,7 +1,6 @@
 {
   build-toolbox = import ./build-toolbox;
   checked-shell-script = import ./checked-shell-script;
-  ghr = import ./ghr;
   gitignore = import ./gitignore.nix;
   haskell-packages = import ./haskell-packages.nix;
   postgresql-default = import ./postgresql-default.nix;

nix/overlays/ghr/default.nix

@@ -1,7 +0,0 @@
-self: super:
-# Overlay that adds `ghr`: Upload multiple artifacts to GitHub Release in
-# parallel, http://tcnksm.github.io/ghr/
-
-{
-  ghr = super.callPackage ./ghr.nix { };
-}

nix/overlays/ghr/ghr.nix

@@ -1,18 +0,0 @@
-{ buildGoModule, fetchFromGitHub }:
-
-buildGoModule rec {
-  pname = "ghr";
-  version = "0.14.0";
-
-  src = fetchFromGitHub {
-    rev = "v${version}";
-    owner = "tcnksm";
-    repo = "ghr";
-    sha256 = "1jjc3bwmyw831r1ayic1f1ysh5ggm88aszbndm0swg8byhz56pd4";
-  };
-
-  vendorSha256 = "06cbhsnxv4gisnwrhw61af7rpv2a9slf9z2wbn79r91xzkh51vzr";
-
-  # Disabling tests, as they require a GitHub API token
-  doCheck = false;
-}