Server side mutation errors are not reported in the explorer

**Intended outcome:**

Server side error when executing a mutation shows up in the result pane.

**Actual outcome:**

The execute button hangs forever and the error is reported as an uncaught in the main console log, nothing shows in the explorer result pane.

This seems to be limited only to Mutations, same works just fine for Queries.
Also, using the Apollo Studio webapp works correctly for both Queries & Mutations.

**How to reproduce the issue:**

1. Open the explorer tab
2. Execute a mutation that results in a server error

**Desktop (please complete the following information):**

- OS: Linux
- Browser: Brave
- Browser version: 1.61.109
- Extension version 4.3.1

Start in the explorer tab's mutation execution path and reproduce a mutation that returns a server error, comparing it with the working query behavior. Done means the execute button no longer hangs and the server-side error appears in the explorer result pane instead of only the main console.

Written by the indexing model from the issue text.