.Net: Bugfix for Mistral tool type parameter (#12310)

### Motivation and Context

- Fixes #11101

Author: rogerbarreto

dotnet/src/Connectors/Connectors.MistralAI.UnitTests/Services/MistralAIChatCompletionServiceTests.cs

@@ -138,6 +138,7 @@ static void MutateChatHistory(AutoFunctionInvocationContext context, Func<AutoFu
         Assert.Equal("assistant", assistantSecondResponse.GetProperty("role").GetString());
         Assert.Equal("ejOH4Z1A2", assistantSecondResponse.GetProperty("tool_calls")[0].GetProperty("id").GetString());
         Assert.Equal("WeatherPlugin-GetWeather", assistantSecondResponse.GetProperty("tool_calls")[0].GetProperty("function").GetProperty("name").GetString());
+        Assert.Equal("function", assistantSecondResponse.GetProperty("tool_calls")[0].GetProperty("type").GetString());
 
         var functionResult = messages[4];
         Assert.Equal("tool", functionResult.GetProperty("role").GetString());
@@ -211,6 +212,7 @@ static void MutateChatHistory(AutoFunctionInvocationContext context, Func<AutoFu
         Assert.Equal("assistant", assistantSecondResponse.GetProperty("role").GetString());
         Assert.Equal("u2ef3Udel", assistantSecondResponse.GetProperty("tool_calls")[0].GetProperty("id").GetString());
         Assert.Equal("WeatherPlugin-GetWeather", assistantSecondResponse.GetProperty("tool_calls")[0].GetProperty("function").GetProperty("name").GetString());
+        Assert.Equal("function", assistantSecondResponse.GetProperty("tool_calls")[0].GetProperty("type").GetString());
 
         var functionResult = messages[4];
         Assert.Equal("tool", functionResult.GetProperty("role").GetString());

dotnet/src/Connectors/Connectors.MistralAI/Client/MistralToolCall.cs

@@ -13,6 +13,9 @@ internal sealed class MistralToolCall
     [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
     public string? Id { get; set; }
 
+    [JsonPropertyName("type")]
+    public string Type { get; set; } = "function";
+
     [JsonPropertyName("function")]
     [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
     public MistralFunction? Function { get; set; }

dotnet/src/IntegrationTests/Connectors/MistralAI/ChatCompletion/MistralAIChatCompletionTests.cs

@@ -507,7 +507,7 @@ public async Task ValidateGetChatMessageContentsWithAutoInvokeAndMultipleCallsAs
         var executionSettings = new MistralAIPromptExecutionSettings { ToolCallBehavior = MistralAIToolCallBehavior.AutoInvokeKernelFunctions };
         var result1 = await service.GetChatMessageContentsAsync(chatHistory, executionSettings, kernel);
         chatHistory.AddRange(result1);
-        chatHistory.Add(new ChatMessageContent(AuthorRole.User, "What is the weather like in Marseille?"));
+        chatHistory.Add(new ChatMessageContent(AuthorRole.User, "What is the weather temperature in Marseille?"));
         var result2 = await service.GetChatMessageContentsAsync(chatHistory, executionSettings, kernel);
 
         // Assert