从dotdeb在Debian 6上安装PHP 5.4

在dotdeb.org上，据说：

2015年2月18日，PHP小组发布了PHP 5.4.38。

相应的软件包现在可以在Dotdeb:上获得

适用于amd64和i386上的Debian 7"Wheezy"和Debian 6"Squeeze"架构。

这很酷，但我已经将它们添加到了源列表中，用apt-get update更新了包列表，并使apt-get upgrade。。。但PHP仅更新为5.3.29-1~dotdeb.0

知道为什么以及如何修复它吗？与他们完全没有联系。

我的资源列表：

deb http://packages.dotdeb.org squeeze all
deb-src http://packages.dotdeb.org squeeze all
deb http://packages.dotdeb.org squeeze-php54 all
deb-src http://packages.dotdeb.org squeeze-php54 all

命令和输出：

apt-get update
Hit http://packages.dotdeb.org squeeze Release.gpg
Ign http://packages.dotdeb.org squeeze/all Translation-en_US
Hit http://packages.dotdeb.org squeeze-php54 Release.gpg
Ign http://packages.dotdeb.org squeeze-php54/all Translation-en_US
Hit http://packages.dotdeb.org squeeze Release
Hit http://packages.dotdeb.org squeeze-php54 Release
Ign http://packages.dotdeb.org squeeze/all Packages/DiffIndex
Ign http://packages.dotdeb.org squeeze/all Sources/DiffIndex
Ign http://packages.dotdeb.org squeeze-php54/all Packages/DiffIndex
Ign http://packages.dotdeb.org squeeze-php54/all Sources/DiffIndex
Hit http://packages.dotdeb.org squeeze/all Packages
Hit http://packages.dotdeb.org squeeze/all Sources
Hit http://packages.dotdeb.org squeeze-php54/all Packages
Hit http://packages.dotdeb.org squeeze-php54/all Sources
Reading package lists... Done
apt-get upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages have been kept back:
  libapache2-mod-php5 mysql-client php-pear php5 php5-cli php5-common
  php5-curl php5-dev php5-gd php5-imagick php5-mcrypt php5-mysql php5-sqlite
0 upgraded, 0 newly installed, 0 to remove and 13 not upgraded.