fix: correct omitempty tag in VariableFilter.EnvironmentScope field

mentioned in commit 88f856ff

mentioned in merge request gitlab-org/cli!2607 (merged)

mentioned in merge request gitlab-com/gl-infra/woodhouse!738

mentioned in merge request sickit/token-operator!40 (merged)

mentioned in merge request hojerdev/git-sync!72

mentioned in merge request gitlab-org/release-tools!4633

mentioned in merge request gitlab-com/gl-infra/oncall-robot-assistant!110

mentioned in merge request schober-server/kubernetes/images/gitlab-token-refresher!37

mentioned in merge request fforster/epic-update!48 (merged)

mentioned in merge request fforster/gitlab-mcp!219 (merged)

mentioned in merge request gitlab-com/gl-infra/autolabels!144 (merged)

mentioned in merge request gitlab-com/gl-infra/ringctl!424 (merged)

mentioned in merge request gitlab-com/gl-infra/platform/runway/runwayctl!1443 (merged)

mentioned in merge request ydkn/gitlab-runner-cleanup!46 (closed)