test(nix-bindings-store): accept new Nix error format for invalid system builds

Nix changed "required system or feature not available" to "platform mismatch".

nix-bindings-store/src/store.rs

@@ -788,7 +788,8 @@ mod tests {
             Err(e) => e.to_string(),
         };
         assert!(
-            err.contains("required system or feature not available"),
+            err.contains("required system or feature not available")
+                || err.contains("platform mismatch"),
             "Error should mention system not available, got: {}",
             err
         );