gitea doctor failed at checking and fixing 'delete-orphaned-repos', because table name 'user' needs quoting to be correctly recognized by at least PostgreSQL. fixes #28199
the iteration will run until finished atm. this changes it by checking if if the context got canceled before each run of a loop sequence is executed [View this pull with now whitespace](https://github.com/go-gitea/gitea/pull/27710/files?diff=unified&w=1)
to address #27273 replace #24873