gitlab-ci: Don't hardcode release version

Thanks to Jan Tojnar who found a work-around:

https://gitlab.gnome.org/GNOME/calls/-/merge_requests/770

This uses the artifacts:reports:dotenv feature to pass environment
variables to the deploy stage:

https://docs.gitlab.com/ci/variables/#pass-an-environment-variable-to-another-job

I didn't test the change with the sandbox yet.

.gitlab-ci.yml

@@ -2,7 +2,7 @@ include:
   - component: "gitlab.gnome.org/GNOME/citemplates/release-service@master"
     inputs:
       dist-job-name: "dist"
-      tarball-artifact-path: "libxml2-dist/libxml2-2.15.0.tar.xz"
+      tarball-artifact-path: "${TARBALL_ARTIFACT_PATH}"
 
 .test:
   image: registry.gitlab.gnome.org/gnome/libxml2
@@ -300,9 +300,12 @@ dist:
   image: registry.gitlab.gnome.org/gnome/libxml2
   script:
     - sh .gitlab-ci/dist.sh
+    - echo "TARBALL_ARTIFACT_PATH=$(ls libxml2-dist/*.tar.xz)" >> build.env
   artifacts:
     paths:
       - libxml2-dist/*.tar.xz
+    reports:
+      dotenv: build.env
 
 pages:
   script:

MAINTAINERS.md

@@ -52,9 +52,6 @@ You can get started by running
 
 Update the version number in `VERSION` if you haven't done so already.
 
-IMPORTANT: Update the version number of `tarball-artifact-path` in
-`.gitlab-ci.yml`. This must be done manually for now.
-
 ### Commit and verify tarball
 
 Release tarballs are generated with a CI job and the `.gitlab-ci/dist.sh`