Add info about o3-mini for Copilot Free (#54266)

Author: saritai

content/copilot/managing-copilot/managing-copilot-as-an-individual-subscriber/about-github-copilot-free.md

@@ -29,7 +29,7 @@ topics:
   * Custom instructions (**only in {% data variables.product.prodname_vs %}, {% data variables.product.prodname_vscode_shortname %}, and {% data variables.product.prodname_dotcom_the_website %}**)
   * Prompt files (**only in {% data variables.product.prodname_vscode_shortname %}**)
 * Block suggestions matching public code
-* Access to the {% data variables.copilot.copilot_claude_sonnet %} and {% data variables.copilot.copilot_gemini_flash %} models
+* Access to the {% data variables.copilot.copilot_claude_sonnet %}, {% data variables.copilot.copilot_gemini_flash %} and o3-mini models
 * Access to {% data variables.product.prodname_copilot_extensions_short %} in {% data variables.product.prodname_vscode %}, {% data variables.product.prodname_vs %}, JetBrains IDEs, {% data variables.product.prodname_dotcom_the_website %}, and {% data variables.product.prodname_mobile %}
 
 ## What are the limitations of {% data variables.product.prodname_copilot_free_short %}?