The external Kernel:* and internal Devel:Kernel:* projects stopped updating
recently, because the upload script is receiving HTTP 500 now. It can also be
reproduced by curl:

$ curl -n -T data.xml
'https://api.suse.de/source/home:michal-m:test/_meta?force=1'
500 Internal Server Error
If you are the administrator of this website, then please read this web
application's log file and/or the web server's log file to find out what went
wrong.

It does work with 'osc api -M PUT -f data.xml'. The difference turns out to be
the Content-type header, which osc sends. I will fix the script to also send
the header, but please fix the server so that it is not as picky. Ironically,
the header value is not used anywhere: osc sends application/octet-stream when
uploading XML and the server accepts anything:

$ curl -n -T data.xml -H 'Content-type: yada/dada'
'https://api.suse.de/source/home:michal-m:test/_meta?force=1'
<status code="ok">
  <summary>Ok</summary>
</status>