"Unacceptable TLS certificate" when updating flatpaks with extra-data

[Vadim Rutkovsky]

Hi,

I've been using Fedora Silverblue 29 and after a few updates I've hit
a weird issue:
```
$ flatpak --user -y update
Looking for updates...
Updating in user:
com.skype.Client/x86_64/stable      flathub 6b76db7937a0
com.visualstudio.code/x86_64/stable flathub 0bab3d6991ee
  new dbus access: org.freedesktop.Flatpak
Updating for user: com.skype.Client/x86_64/stable from flathub
[#=                  ] Downloading files: 1/1 569 bytes (569 bytes/s)
Error: Failed to update com.skype.Client/x86_64/stable: While
downloading https://repo.skype.com/deb/pool/main/s/skypeforlinux/skypeforlinux_8.29.0.50_amd64.deb:
Unacceptable TLS certificate
Updating for user: com.visualstudio.code/x86_64/stable from flathub
[#=                  ] Downloading files: 1/1 569 bytes (569 bytes/s)
Error: Failed to update com.visualstudio.code/x86_64/stable: While
downloading https://vscode-update.azurewebsites.net/1.27.1/linux-x64/stable:
Unacceptable TLS certificate
error: There were one or more errors
```
These files can however be correctly downloaded with `curl` and `wget`.

Flatpaks without extra-data set download just fine.

Is there some cache (afaik libsoup is used there) I need to cleanup to
make it work?

-- 
Cheers,
  Vadim