docs: fix incorrect model.fallback to model.fallbacks in Ollama config (#9384) (#9749)

Both English and Chinese documentation had incorrect configuration template
using 'fallback' instead of 'fallbacks' in agents.defaults.model config.

Co-authored-by: damaozi <1811866786@qq.com>

docs/providers/ollama.md

@@ -149,7 +149,7 @@ Once configured, all your Ollama models are available:
     defaults: {
       model: {
         primary: "ollama/llama3.3",
-        fallback: ["ollama/qwen2.5-coder:32b"],
+        fallbacks: ["ollama/qwen2.5-coder:32b"],
       },
     },
   },

docs/zh-CN/providers/ollama.md

@@ -156,7 +156,7 @@ export OLLAMA_API_KEY="ollama-local"
     defaults: {
       model: {
         primary: "ollama/llama3.3",
-        fallback: ["ollama/qwen2.5-coder:32b"],
+        fallbacks: ["ollama/qwen2.5-coder:32b"],
       },
     },
   },