contrib/actions: drop version pin on libncurses-dev

Fixes unmet dependencies:

 The following packages have unmet dependencies:
 libncurses5-dev : Depends: libtinfo5 (= 6.1-1ubuntu1.18.04) but 6.2-0ubuntu2 is to be installed
                   Depends: libncurses5 (= 6.1-1ubuntu1.18.04) but 6.2-0ubuntu2 is to be installed
                   Depends: libtinfo-dev (= 6.1-1ubuntu1.18.04)
 python : PreDepends: python-minimal (= 2.7.15~rc1-1) but it is not going to be installed
          Depends: libpython-stdlib (= 2.7.15~rc1-1) but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

Switch to apt-get, because it has a stable API. Same as ca7a8ff5.

contrib/actions/install-dependencies.sh

@@ -4,7 +4,7 @@ set -e
 
 cp contrib/actions/sources.list /etc/apt/sources.list
 rm -rf /etc/apt/sources.list.d
-apt update
-apt install git subversion build-essential python gawk unzip libncurses5-dev zlib1g-dev libssl-dev wget time
-apt clean
+apt-get update
+apt-get install git subversion build-essential python gawk unzip libncurses-dev zlib1g-dev libssl-dev wget time
+apt-get clean
 rm -rf /var/lib/apt/lists/*