fix: gpt-5-chat is not a reasoning model

* Exclude GPT-5-Chat 

Exclude GPT-5-Chat. It is not a reasoning model.

* [pre-commit.ci lite] apply automatic fixes

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Co-authored-by: pre-commit-ci-lite[bot] <117423508+pre-commit-ci-lite[bot]@users.noreply.github.com>

lua/avante/providers/openai.lua

@@ -67,7 +67,8 @@ function M.get_user_message(opts)
 end
 
 function M.is_reasoning_model(model)
-  return model and (string.match(model, "^o%d+") ~= nil or string.match(model, "gpt%-5") ~= nil)
+  return model
+    and (string.match(model, "^o%d+") ~= nil or (string.match(model, "gpt%-5") ~= nil and model ~= "gpt-5-chat"))
 end
 
 function M.set_allowed_params(provider_conf, request_body)