Some flatpaks broke with the move to meson [1], which doesn't set
trust_paths automatically (the autoconf based build system did, by
checking what files were available on the system - it picked
/etc/ssl/certs/ca-certificates.crt for our build).
p11-kit on the host system matters for flatpaks, as seen in [2].
Thanks to steinex for coming up with the solution. [3] was a fix for the
same issue, but with autoconf.
[1] 7377f185fc
[2] https://github.com/p11-glue/p11-kit/issues/275
[3] 27d5c551b4
943e49052c