fix: make gpg configuration to work

install also `gpg-agent` as it's needed by gpg to import keys.
closes #48

Signed-off-by: Sylvain Desbureaux <sylvain.desbureaux@orange.com>

templates/gitlab-ci-semrel.yml

@@ -804,7 +804,7 @@ stages:
     - !reference [.semrel-scripts]
     - install_ca_certs "${CUSTOM_CA_CERTS:-$DEFAULT_CA_CERTS}"
     # install git and OpenSSH
-    - maybe_install_packages ca-certificates git openssh-client gpg
+    - maybe_install_packages ca-certificates git openssh-client gpg gpg-agent
     - maybe_install_yq
     - cd "${SEMREL_CONFIG_DIR}"
     - prepare_semantic_release