Add new supported github-copilot models to builtin conf

[zikajk]

• I added a entry in changelog under unreleased section.

[Copilot]

Pull request overview

This PR adds support for new AI models to the github-copilot provider configuration, expanding the available model options for users with GitHub Copilot access. The changes include adding GPT-5.1 variants, GPT-5-codex, and Gemini-3-pro to both the configuration and integration tests.

• Added 5 new models to the github-copilot provider: gpt-5.1, gpt-5.1-codex, gpt-5.1-codex-mini, gpt-5-codex, and gemini-3-pro
• Updated integration tests to verify the new models are properly initialized
• Added a changelog entry documenting the new model support

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/eca/config.clj	Added 5 new model entries to the github-copilot provider configuration
integration-test/integration/initialize_test.clj	Updated both test cases to include the new models in expected model lists
CHANGELOG.md	Added changelog entry for the new models (contains a spelling error)

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[Copilot]

"Github" should be spelled "GitHub" (with a capital H).

Suggested change

	- Add new OpenAI and Gemini models to Github config.
	- Add new OpenAI and Gemini models to GitHub config.

[zikajk]

@ericdallo There is a problem with Gemini responses that should be fixed first:

'https://api.githubcopilot.com/chat/completions'
[OPENAI-CHAT] 4813 Unexpected response status: %s body: %s 400 {"error":{"message":"invalid request body","code":"invalid_request_body"}}

[ericdallo]

Hum, we need to understand if we need to change the body for that model, maybe do in other PR the gemini?

[zikajk]

Agree, done :-)