Slow fetching of https://gerrit.libreoffice.org/core?

[Stephan Bergmann]

More often than not, trying to do a LibreOffice Flatpak build on Flathub 
fails because the step that fetches the 
<https://gerrit.libreoffice.org/core?> git repo times out.  See e.g. 
<https://flathub.org/builds/#/builders/27/builds/44525> and 
<https://flathub.org/builds/#/builders/27/builds/44278>, with the 
relevant log output being

> ]2;flatpak-builder: Downloading gvfs]2;flatpak-builder: Downloading krb5]2;flatpak-builder: Downloading libreofficeFetching full git repo https://gerrit.libreoffice.org/core?
> command timed out: 3600 seconds without output running [b'flatpak-builder', b'--download-only', b'--no-shallow-clone', b'--allow-missing-runtimes', b'--state-dir=/srv/buildbot/sources', b'/srv/buildbot/sources/.builddir', b'org.libreoffice.LibreOffice.json'], attempting to kill

I'm not sure whether the best place to do something about this would be 
the serving libreoffice.org side, or the receiving flathub.org side, or 
even my choice of <https://gerrit.libreoffice.org/core?> git repo URL at 
<https://git.libreoffice.org/core/+/0f288cf2df790d5cd13511471e0216c46c0564b5%5E!/> 
"solenv/flatpak-manifest.in: Merge 'Switch git repo URL from git: to 
https:'"?