Adjust fuzzers group to respect build variables

Avoid including targets that might not be present.

Bug: None
Change-Id: I439a3ff4e34337ecd64c6986edffcaa0843611cc
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/360121
Commit-Queue: Christoffer Dewerin <jansson@webrtc.org>
Auto-Submit: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Christoffer Dewerin <jansson@webrtc.org>
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#42820}