etc/distro/keys/tails.key: signing key changed again...

Repro notes per last update at linuxboot#1631 (comment)

rm -rf /tmp/tails-signing/
wget -q https://tails.boum.org/tails-signing.key -O tails-signing.key
mkdir -p /tmp/tails-signing/
gpg --home /tmp/tails-signing/ --import tails-signing.key
gpg --home /tmp/tails-signing/ --export --armor --export-options export-minimal,export-clean [email protected] > ~/heads/initrd/etc/distro/keys/tails.key

Signed-off-by: Thierry Laurion <[email protected]>