nixos/modules: Replace all nested types.either's with types.oneOf's

nixos/modules/system/boot/systemd-unit-options.nix

@@ -226,7 +226,7 @@ in rec {
 
     environment = mkOption {
       default = {};
-      type = with types; attrsOf (nullOr (either str (either path package)));
+      type = with types; attrsOf (nullOr (oneOf [ str path package ]));
       example = { PATH = "/foo/bar/bin"; LANG = "nl_NL.UTF-8"; };
       description = "Environment variables passed to the service's processes.";
     };

nixos/modules/system/boot/systemd.nix

@@ -520,7 +520,7 @@ in
     };
 
     systemd.globalEnvironment = mkOption {
-      type = with types; attrsOf (nullOr (either str (either path package)));
+      type = with types; attrsOf (nullOr (oneOf [ str path package ]));
       default = {};
       example = { TZ = "CET"; };
       description = ''