apt-get upgrade show it will upgrade xwiki-enterprise-mysql-common and begins. It spits out a warning, but afterwards, xwiki-enterprise-mysql-common is still an upgrade candidate, probably due to the warning:
~# apt-get upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages will be upgraded:
1 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Need to get 0 B/3,726 B of archives.
After this operation, 0 B of additional disk space will be used.
Do you want to continue [Y/n]?
WARNING: The following packages cannot be authenticated!
Install these packages without verification [y/N]? y
dpkg: warning: parsing file '/var/lib/dpkg/tmp.ci/control' near line 6 package 'xwiki-enterprise-mysql-common':
`Depends' field, reference to `xwiki-enterprise-common':
implicit exact match on version number, suggest using `=' instead
(Reading database ... 64735 files and directories currently installed.)
Preparing to replace xwiki-enterprise-mysql-common 4.1.2 (using .../xwiki-enterprise-mysql-common_4.1.2_all.deb) ...
Unpacking replacement xwiki-enterprise-mysql-common ...
Setting up xwiki-enterprise-mysql-common (4.1.2) ...
dbconfig-common: writing config to /etc/dbconfig-common/xwiki.conf
dbconfig-common: flushing administrative password
This process can be repeated ad infinitum.
Also, as can be seen from the output, the packages can not be authenticated due to a missing key for the repo/releaser I could not find.