fix: resolve pre-existing typecheck error in error.test.ts

Add default value for `url` parameter in `makeAPICallError` helper
to satisfy `APICallError` constructor's required `string` type.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: anandgupta42

packages/opencode/test/provider/error.test.ts

@@ -17,7 +17,7 @@ function makeAPICallError(opts: {
     statusCode: opts.statusCode,
     responseBody: opts.responseBody,
     isRetryable: opts.isRetryable ?? false,
-    url: opts.url,
+    url: opts.url ?? "",
     responseHeaders: opts.responseHeaders,
     requestBodyValues: {},
   })