infra/config: Set fallback-on-exec-error on chromeos builder

This is to allow fallback when remote action fails in chromeos builders.

ChromeOS' compiler_wrapper sometimes crashed and we need to allow
fallback for that before disabling fallback in siso by default.

Bug: 406369220, 377426017
Change-Id: Ifb59725eaef450114057b22b51fd5ba0e56ada2f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6438679
Commit-Queue: Takuto Ikuta <tikuta@chromium.org>
Reviewed-by: Fumitoshi Ukai <ukai@google.com>
Commit-Queue: Junji Watanabe <jwata@google.com>
Reviewed-by: Junji Watanabe <jwata@google.com>
Auto-Submit: Takuto Ikuta <tikuta@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1444594}