Add missing BUILD.gn dep on absl AnyInvocable.

This missing dep was found when building this code in a downstream repo.

Bug: b/423646186
Change-Id: I94f5cf1dfd4d65a3042eabee05720c03e7bf720f
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/417320
Commit-Queue: Rasmus Brandt <brandtr@webrtc.org>
Reviewed-by: Åsa Persson <asapersson@webrtc.org>
Commit-Queue: Åsa Persson <asapersson@webrtc.org>
Auto-Submit: Rasmus Brandt <brandtr@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#45942}