core-services-01(autodeploy): enable default /var/src usage through systemd tmp filesystem and force creation of sentinel file

.drone.yml

@@ -14,7 +14,6 @@ steps:
 - name: Build core-services-01 configuration
   commands:
     - "export NIX_PATH=nixpkgs=/var/nixpkgs"
-    - "mkdir -p /var/src && touch /var/src/.populate"
     - "echo Building core-services-01 && nix-build krops.nix -A test-core-services-01 && ./result"
 
 ...

krops.nix

@@ -25,6 +25,7 @@ in
     test-core-services-01 = pkgs.krops.writeTest "test-core-services-01" {
       source = source "core-services-01";
       target = "localhost";
+      force = true; # force create the sentinel file.
     };
 
   }

machines/core-services-01/nix/sources.json

@@ -14,7 +14,7 @@
     "klubrz-nur": {
         "branch": "main",
         "repo": "https://git.rz.ens.wtf/Klub-RZ/nur",
-        "rev": "3f6a760254c3259e6abc0dcf443c533cd999a739",
+        "rev": "901e08a94819f07499ec6cfbea1e24808e19e4b6",
         "type": "git"
     },
     "niv": {