Add nix build action (#69)

* Add nix build action

As mentioned in #67, this action
builds the default package from the nix flake on pull requests and commits
on main. This should prevent lockfile mismatches in the future :)
(especially because the nix build is currently broken due to openssl vendoring,
I will try to address that soon)

* flake: disable openssl vendoring

.github/workflows/nix.yml

@@ -0,0 +1,15 @@
+on:
+  pull_request:
+  push:
+    branches: [main]
+
+jobs:
+  build:
+    name: Build nix targets
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Install Nix
+        uses: DeterminateSystems/nix-installer-action@v3
+      - name: Build default package
+        run: nix build

flake.nix

@@ -40,6 +40,7 @@
         };
         devShells.default = pkgs.mkShell {
           name = "rust devShell";
+          OPENSSL_NO_VENDOR = 1;
           buildInputs = with pkgs;
           with pkgs.rustPlatform; [
             cargo
@@ -59,6 +60,7 @@
             cargoDeps = final.rustPlatform.importCargoLock {
               lockFile = self + "/Cargo.lock";
             };
+            OPENSSL_NO_VENDOR = 1;
           });
         };