Add crates/assistant_tools/src/evals/fixtures to file_scan_exclusions (#32211)

Particularly got tired of `disable_cursor_blinking/before.rs` (an old
copy of `editor.rs`) showing up in tons of searches

Release Notes:

- N/A

.zed/settings.json

@@ -47,6 +47,7 @@
   "remove_trailing_whitespace_on_save": true,
   "ensure_final_newline_on_save": true,
   "file_scan_exclusions": [
+    "crates/assistant_tools/src/evals/fixtures",
     "crates/eval/worktrees/",
     "crates/eval/repos/",
     "**/.git",