Since libical was updated to 2.0.0, the tzdata path substition has had
no effect due to changes in the upstream source code. [0]

So, libical probably can't find the time zone file, and it doesn't keep
a reference to tzdata.

I assume it needs to be fixed? But what is the impact, if we never
noticed? :)

[0] Commit 2b193389d243c469e159d0ab5dfc86b5867db05d, only two days after
the substitution was added.