ollama: Fix build with default features (#29502)

The `ollama` crate has a `use schemars::JsonSchema` statement even when
building with default features, which doesn't include the `schemars`
crate.

Release Notes:

- N/A

crates/ollama/src/ollama.rs

@@ -1,7 +1,6 @@
 use anyhow::{Context as _, Result, anyhow};
 use futures::{AsyncBufReadExt, AsyncReadExt, StreamExt, io::BufReader, stream::BoxStream};
 use http_client::{AsyncBody, HttpClient, Method, Request as HttpRequest, http};
-use schemars::JsonSchema;
 use serde::{Deserialize, Serialize};
 use serde_json::{Value, value::RawValue};
 use std::{convert::TryFrom, sync::Arc, time::Duration};
@@ -39,7 +38,8 @@ impl From<Role> for String {
     }
 }
 
-#[derive(Clone, Serialize, Deserialize, Debug, Eq, PartialEq, JsonSchema)]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
+#[derive(Clone, Serialize, Deserialize, Debug, Eq, PartialEq)]
 #[serde(untagged)]
 pub enum KeepAlive {
     /// Keep model alive for N seconds