Variable expansion not working for CI_COMMIT_TITLE in rules or only/except

Hi,

I want to use a global variable VERSIONUPDATE_MSG_PREFIX from gitlab-ci.yml like except:
variables: - '$CI_COMMIT_TITLE && ($CI_COMMIT_TITLE =~ /^$VERSIONUPDATE_MSG_PREFIX/)'

or rules:

• if: $CI_COMMIT_TITLE && ($CI_COMMIT_TITLE =~ /^$MY_IGNORE/) when: never

but doesn't work. It works only, if I use a fixed string.

How can I use a global variable?