collab: Attach GitHub login to LLM spans (#16316)

This PR updates the LLM service to include the GitHub login on its
spans.

We need to pass this information through on the LLM token, so it will
temporarily be `None` until this change is deployed and new tokens have
been issued.

Release Notes:

- N/A

crates/collab/src/llm.rs

@@ -140,6 +140,7 @@ async fn validate_api_token<B>(mut req: Request<B>, next: Next<B>) -> impl IntoR
 
             tracing::Span::current()
                 .record("user_id", claims.user_id)
+                .record("login", claims.github_user_login.clone())
                 .record("authn.jti", &claims.jti);
 
             req.extensions_mut().insert(claims);