Use openssl_3_0 and niv update all deps (#50)

It appears that recent Ubuntu distros don't include `openssl-1.1.1` by default any more (fixes #48), this PR adopts 3.0.

v3.0 of `openssl` has been released on 8 Sept 2021, so it should be widespread enough in recent distributions.

Also bumps:
- `nix` deps (e.g. `release-22.05`)
- `cargo` deps
- some GH actions

.github/workflows/nix-build.yml

@@ -6,8 +6,8 @@ jobs:
   all-targets:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v2.3.4
-    - uses: cachix/install-nix-action@v16
+    - uses: actions/checkout@v3
+    - uses: cachix/install-nix-action@v17
       with:
         nix_path: nixpkgs=channel:nixos-unstable
     - run: nix-build