.Net: Fix unit tests to check for security property (#9635)

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### Contribution Checklist

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- [ ] The code builds clean without any errors or warnings
- [ ] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
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raises no violations
- [ ] All unit tests pass, and I have added new tests where possible
- [ ] I didn't break anyone 😄

dotnet/src/Functions/Functions.UnitTests/OpenApi/Extensions/OpenApiKernelExtensionsTests.cs

@@ -294,8 +294,8 @@ public async Task ItShouldReplicateMetadataToOperationAsync(string documentFileN
         Assert.Equal(["https://my-key-vault.vault.azure.net"], serverUrls);
         var info = additionalProperties["info"] as RestApiInfo;
         Assert.NotNull(info);
-        var security = additionalProperties["info"] as List<RestApiSecurityRequirement>;
-        Assert.Null(security);
+        var security = additionalProperties["security"] as List<RestApiSecurityRequirement>;
+        Assert.NotNull(security);
 
         // Assert Operation Extension keys
         var operationExtensions = additionalProperties["operation-extensions"] as Dictionary<string, object?>;

dotnet/src/Functions/Functions.UnitTests/OpenApi/OpenApiKernelPluginFactoryTests.cs

@@ -285,8 +285,8 @@ public async Task ItShouldReplicateMetadataToOperationAsync(string documentFileN
         Assert.Equal(["https://my-key-vault.vault.azure.net"], serverUrls);
         var info = additionalProperties["info"] as RestApiInfo;
         Assert.NotNull(info);
-        var security = additionalProperties["info"] as List<RestApiSecurityRequirement>;
-        Assert.Null(security);
+        var security = additionalProperties["security"] as List<RestApiSecurityRequirement>;
+        Assert.NotNull(security);
 
         // Assert Operation Extension keys
         var operationExtensions = additionalProperties["operation-extensions"] as Dictionary<string, object?>;