This change was previously part of
fb1c0a4c48, which got reverted due to an
issue
with the compositor channel.
Split this change out into a separate PR, as it probably should have
been in the first place. Presumably it was one change before, since
serialization of crossbeam generic channels in single-process mode was
not implemented yet at the time.
Testing: Covered by existing tests. No custom callbacks involved.
Part of #38912
Signed-off-by: Jonathan Schwender <schwenderjonathan@gmail.com>