Drop NixOS 20.09 support

CHANGELOG.md

@@ -2,6 +2,11 @@
 
 ## Next
 
+### Removed
+
+ - NixOS 20.09 support. Its docker-compose does not support the
+   `networks.<name>.name` option, which is important in later versions.
+
 ### Changed
 
 * Healthcheck-based dependencies in `service.depends_on`.

nix/ci.nix

@@ -5,13 +5,6 @@ let
 in
 
 dimension "Nixpkgs version" {
-    # avoid bitrotting the docker support (as opposed to podman)
-    "nixos-20_09" = {
-      nixpkgsSource = "nixos-20.09";
-      enableDoc = true;
-      dockerSupportsSystemd = true;
-      nixosHasPodmanDockerSocket = false;
-    };
     "nixos-22_05" = {
       nixpkgsSource = "nixos-22.05";
       enableDoc = true;

nix/sources.json

@@ -11,18 +11,6 @@
         "url": "https://github.com/nmattia/niv/archive/fad2a6cbfb2e7cdebb7cb0ad2f5cc91e2c9bc06b.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
-    "nixos-20.09": {
-        "branch": "nixos-20.09",
-        "description": "Nix Packages collection",
-        "homepage": null,
-        "owner": "NixOS",
-        "repo": "nixpkgs",
-        "rev": "0cfe5377e8993052f9b0dd56d058f8008af45bd9",
-        "sha256": "0i3ybddi2mrlaz3di3svdpgy93zwmdglpywih4s9rd3wj865gzn1",
-        "type": "tarball",
-        "url": "https://github.com/NixOS/nixpkgs/archive/0cfe5377e8993052f9b0dd56d058f8008af45bd9.tar.gz",
-        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
-    },
     "nixos-22.05": {
         "branch": "nixos-22.05",
         "description": "Nix Packages collection",