docs(tools): minor grammar fix (#10097)

## Background

https://www.merriam-webster.com/grammar/when-to-use-its-vs-its

## Summary

it's -> its

Author: neallseth

content/docs/03-ai-sdk-core/15-tools-and-tool-calling.mdx

@@ -58,7 +58,7 @@ With the `stopWhen` setting, you can enable multi-step calls in `generateText` a
   results.
 </Note>
 
-By default, when you use `generateText` or `streamText`, it triggers a single generation. This works well for many use cases where you can rely on the model's training data to generate a response. However, when you provide tools, the model now has the choice to either generate a normal text response, or generate a tool call. If the model generates a tool call, it's generation is complete and that step is finished.
+By default, when you use `generateText` or `streamText`, it triggers a single generation. This works well for many use cases where you can rely on the model's training data to generate a response. However, when you provide tools, the model now has the choice to either generate a normal text response, or generate a tool call. If the model generates a tool call, its generation is complete and that step is finished.
 
 You may want the model to generate text after the tool has been executed, either to summarize the tool results in the context of the users query. In many cases, you may also want the model to use multiple tools in a single response. This is where multi-step calls come in.