add tests for os-release

tests/etc/OSnovaLinux/etc/os-release

+PRETTY_NAME="OSnova Linux (Onyx3 3.0)"
+NAME="OSnova Linux"
+ID=osnova
+ID_LIKE=debian
+ANSI_COLOR="1;31"
+HOME_URL="http://www.nppct.ru/"
+SUPPORT_URL="http://www.nppct.ru/support"
+BUG_REPORT_URL="https://support.nppct.ru"
+VARIANT_ID=onyx3
+VARIANT=Onyx3
+VERSION_ID=3.0
+VERSION_CODENAME=onyx3
+BUILD_ID=3.0
+VERSION="3.0 (Onyx3)"

tests/etc/ROSA13/etc/os-release

+# Standard values
+# Specification: https://www.freedesktop.org/software/systemd/man/os-release.html
+NAME="ROSA Fresh Desktop"
+ID=rosa
+PRETTY_NAME="ROSA Fresh Desktop"
+CPE_NAME="cpe:/o:rosalinux:rosa:13"
+META_CLASS=desktop
+VARIANT_ID=fresh-desktop
+ANSI_COLOR="1;43"
+VERSION="13.0"
+VERSION_ID=13
+VERSION_CODENAME=13.0
+HOME_URL="https://www.rosa.ru"
+# TODO: by far not all icons packages provide an icon "rosa"
+LOGO=rosa
+BUG_REPORT_URL="https://bugzilla.rosa.ru"
+# ROSA-specific values
+ROSA_OS_BRANCH=fresh
+ROSA_OS_PLATFORM="rosa13"
+ROSA_OS_PLATFORM_INTEGER=202510
+ROSA_OS_TYPE=desktop
+ROSA_OS_VERSION=13.0

tests/etc/SberOS/etc/os-release

+PRETTY_NAME="SberOS GNU/Linux (Rolling Release)"
+NAME="SberOS GNU/Linux"
+VERSION_CODENAME="n/a"
+ID=sberos
+HOME_URL="https://sberos.sber.ru/"
+BUG_REPORT_URL="https://bugs.sber.ru"