Update GGML to b6646 (#12245)

Notable EOLs with this change:
- MacOS v12 and v13 are no longer supported (v14+ required)
- AMD gfx900 and gfx906 are no longer supported

llama/llama.cpp/src/llama-chat.h

@@ -49,6 +49,8 @@ enum llm_chat_template {
     LLM_CHAT_TEMPLATE_OPENAI_MOE,
     LLM_CHAT_TEMPLATE_HUNYUAN_DENSE,
     LLM_CHAT_TEMPLATE_KIMI_K2,
+    LLM_CHAT_TEMPLATE_SEED_OSS,
+    LLM_CHAT_TEMPLATE_GROK_2,
     LLM_CHAT_TEMPLATE_UNKNOWN,
 };