May textproc/icu revbump failed to hit finance/ledger32

[Taylor R Campbell <campbell+netbsd-tech-pkg%mumble.net@localhost>]

Back in May, textproc/icu had an update which bumped the shlib version
from 74 to 75:

https://mail-index.netbsd.org/pkgsrc-changes/2024/05/29/msg300987.html

This was followed by a revbump of dependent packages:

https://mail-index.netbsd.org/pkgsrc-changes/2024/05/29/msg300991.html

But it didn't revbump finance/ledger32.

finance/ledger32's bin/ledger executable links against
devel/boost-libs libboost_regex.so, which links against textproc/icu
libicudata.so.

Both dependent packages use buildlink3.mk appropriately:

(devel/boost-libs) .include "../../textproc/icu/buildlink3.mk"
(finance/ledger32) .include "../../devel/boost-libs/buildlink3.mk"

So the revbump should have hit finance/ledger32, but it didn't.  It
hit devel/boost-libs, but not finance/ledger32.

Why did the revbump miss finance/ledger32?  Is there a bug in
pkgtools/revbump's dependent search causing us to miss a class of
dependent packages that need revbumps?