* nanopb 0.4.6.4 with PB_C99_STATIC_ASSERT to avoid depending on C11
* OpenSSL 1.1.1q on windows
* Switched from docker to podman in CI
* Appdir in appimage build container is now in /build/appdir to fix
"Invalid cross-device link" errors in linuxdeploy when appdir is in
mount
* Use python protobuf==3.19.5 in bionic image, which still supports
python 3.6, and on windows where nanopb otherwise has issues
* Purge nanopb_pb2.py to force regeneration of it for possibly different
python protobuf versions in subsequent builds
* FreeBSD needs py39 packages now
