Fix error with releasing CNG images
It's looking for the gitaly version file in the wrong location.
Fixes: https://gitlab.com/gitlab-org/release-tools/issues/331
This changes the variable that gets received on the CNG side, but we already have support for both versions of the Gitaly variable over in CNG (See: https://gitlab.com/gitlab-org/build/CNG/blob/fb4df1986d591921c21715d73910b317dbd12905/.gitlab-ci.yml#L49)