soup: SoupSession is not thread-safe but shared between element instances
See https://libsoup.org/libsoup-3.0/ch02.html#threading
This means that at least with libsoup3 we can't share the session between element instances anymore like this. We would lose connection and cookie sharing at least.
CC @philn who ported to libsoup 3 and also @mcatanzaro because he brought this to my attention via here.
We should probably either move away from libsoup (to...?) or share not just the session between elements but a whole thread plus main context, and dispatch all operations via that main context so the session is only used from a single thread.
Not sure if this should be marked as blocker but AFAIU it's a regression compared to using souphttpsrc
with libsoup2.