fix: label unmarshaling for `BasicMergeRequest` list operations

mentioned in commit 8fb42366

mentioned in merge request gitlab-org/terraform-provider-gitlab!2697 (merged)

mentioned in merge request gitlab-org/cli!2422 (merged)

mentioned in merge request gitlab-com/gl-infra/woodhouse!681 (merged)

mentioned in merge request gitlab-org/release-tools!4498 (merged)

mentioned in merge request gitlab-com/gl-infra/oncall-robot-assistant!104

mentioned in merge request fforster/epic-update!21 (merged)

mentioned in merge request fforster/gitlab-mcp!174 (merged)

mentioned in merge request schober-server/kubernetes/images/gitlab-token-refresher!35

mentioned in merge request gitlab-com/gl-infra/autolabels!102 (merged)

mentioned in merge request gitlab-com/gl-infra/ringctl!357 (merged)

mentioned in merge request gitlab-com/gl-infra/platform/runway/runwayctl!1245 (merged)

mentioned in merge request sickit/token-operator!17 (merged)

mentioned in merge request ydkn/gitlab-runner-cleanup!42

mentioned in merge request hojerdev/git-sync!64 (merged)

mentioned in merge request sue445/tanuki_reminder!262 (merged)

mentioned in merge request sue445/create-merge-request!149 (merged)

mentioned in merge request gitlab-org/container-registry!2558 (merged)