Strengthen integration assertion for error kind extension

Agent-Logs-Url: https://github.com/fsprojects/FSharp.Data.GraphQL/sessions/d64ab4ee-eb67-4b7c-a114-d6ad4b640254

Co-authored-by: xperiandri <2365592+xperiandri@users.noreply.github.com>

Author: Copilot

tests/FSharp.Data.GraphQL.IntegrationTests/OperationErrorTests.fs

@@ -64,3 +64,7 @@ let ``Should map server error extensions and locations into operation result`` (
     error.Extensions.ContainsKey "severity" |> equals true
     error.Extensions.["severity"] |> equals (box 7)
     error.Extensions.ContainsKey "kind" |> equals true
+    match error.Extensions.["kind"] with
+    | :? string as kind -> kind |> equals "Execution"
+    | :? int as kind -> kind |> equals 3
+    | kind -> failwithf "Unexpected kind extension value: %A" kind