CI: Use modern GPG keys

Most of the changes are in GitHub's secret values. The only thing that must
change in the code is the name of the key we search for.

Fixes #1354.

.github/ci.sh

@@ -113,7 +113,7 @@ sign() {
   # statements that could leak GPG-related secrets.
   set +x
   gpg --batch --import <(echo "$SIGNING_KEY")
-  fingerprint="$(gpg --list-keys | grep galois -a1 | head -n1 | awk '{$1=$1};1')"
+  fingerprint="$(gpg --list-keys | grep Galois -a1 | head -n1 | awk '{$1=$1};1')"
   echo "$fingerprint:6" | gpg --import-ownertrust
   gpg --yes --no-tty --batch --pinentry-mode loopback --default-key "$fingerprint" --detach-sign -o "$1".sig --passphrase-file <(echo "$SIGNING_PASSPHRASE") "$1"
   set -x