Bump CORE_NEXT_MINOR after 10.3.x was released

Migrated issue

Reported by: fjgarlin

Related to !134 (merged)

Problem/Motivation

Released 5 minutes ago.

Job detected it here: https://git.drupalcode.org/project/gitlab_templates/-/jobs/868401

Proposed resolution

Bump CORE_NEXT_MINOR after 10.3.x was released