Fix failing nix version test scenario by updating pinned version to 2.18 (#1610)

fix: update nix version from 2.10 to 2.18 in test scenario


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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: Kaniska244 <186041440+Kaniska244@users.noreply.github.com>
Co-authored-by: Kaniska <kaniska244@github.com>

Author: Copilot

test/nix/scenarios.json

@@ -14,7 +14,7 @@
         "features": {
             "nix": {
                 "multiUser": false,
-                "version": "2.10"
+                "version": "2.18"
             }
         }
     },