Make introspection update test idempotence explicit

Agent-Logs-Url: https://github.com/fsprojects/FSharp.Data.GraphQL/sessions/4998e0af-9a24-4088-a9a9-3318b08f3de9

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

Author: Copilot

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

@@ -82,5 +82,9 @@ let ``Update integration introspection file when schema changes`` () =
         let! sourceStream = httpClient.GetStreamAsync("/")
         let! wasUpdated = updateIntrospectionFileAsync CancellationToken.None sourceStream
         Assert.True(File.Exists introspectionFilePath)
-        wasUpdated |> ignore
+        if wasUpdated then
+            let! sourceStreamSecondRun = httpClient.GetStreamAsync("/")
+            use sourceStreamSecondRun = sourceStreamSecondRun
+            let! wasUpdatedSecondRun = updateIntrospectionFileAsync CancellationToken.None sourceStreamSecondRun
+            Assert.False wasUpdatedSecondRun
     }