Import archived GPG key for RPM upgrade test

The upgrade test installs version 2.0.9 which was signed with the old GPG key
before the recent key rotation. Import the archived key (pubring20250228.gpg)
to allow verification of the 2.0.9 package signature during the upgrade test.

Author: fdevans

dockers/install/upgrade-rpm/Dockerfile

@@ -7,6 +7,7 @@ RUN which java
 RUN curl https://raw.githubusercontent.com/rundeck/packaging/main/scripts/rpm-setup.sh 2> /dev/null | bash -s rundeck
 RUN sed -i.bak s/gpgcheck=0/gpgcheck=1/ /etc/yum.repos.d/rundeck.repo
 RUN rpm --import https://raw.githubusercontent.com/rundeck/packaging/main/pubring.gpg
+RUN rpm --import https://raw.githubusercontent.com/rundeck/packaging/main/pubring20250228.gpg
 RUN rpm --import https://docs.rundeck.com/keys/BUILD-GPG-KEY-20230105.key
 
 RUN yum -y install rundeck-cli