Do not enable copilot for always read-only editors (#16356)

Release Notes:

- N/A

crates/assistant/src/inline_assistant.rs

@@ -1109,6 +1109,7 @@ impl InlineAssistant {
                     editor.set_show_gutter(false, cx);
                     editor.scroll_manager.set_forbid_vertical_scroll(true);
                     editor.set_read_only(true);
+                    editor.set_show_inline_completions(false);
                     editor.highlight_rows::<DeletedLines>(
                         Anchor::min()..=Anchor::max(),
                         Some(cx.theme().status().deleted_background),