Disable zeta predictions in assistant completion menu (#23573)

We don't want the zeta predictions entry to show in the assistant
context editor when completing slash commands. Zeta will still make
suggestions in the rest of the context editor, like the other providers
do.

Release Notes:

- N/A

crates/assistant_context_editor/src/context_editor.rs

@@ -15,8 +15,8 @@ use editor::{
         CustomBlockId, FoldId, RenderBlock, ToDisplayPoint,
     },
     scroll::{Autoscroll, AutoscrollStrategy},
-    Anchor, Editor, EditorEvent, ProposedChangeLocation, ProposedChangesEditor, RowExt,
-    ToOffset as _, ToPoint,
+    Anchor, Editor, EditorEvent, MenuInlineCompletionsPolicy, ProposedChangeLocation,
+    ProposedChangesEditor, RowExt, ToOffset as _, ToPoint,
 };
 use editor::{display_map::CreaseId, FoldPlaceholder};
 use fs::Fs;
@@ -220,6 +220,7 @@ impl ContextEditor {
             editor.set_show_wrap_guides(false, cx);
             editor.set_show_indent_guides(false, cx);
             editor.set_completion_provider(Some(Box::new(completion_provider)));
+            editor.set_menu_inline_completions_policy(MenuInlineCompletionsPolicy::Never);
             editor.set_collaboration_hub(Box::new(project.clone()));
             editor
         });