maint: support test releases numbered from .90 for announcements. * maintainer/maint.mk (beta_version_rx, alpha_version_rx): update to use MAJOR.MINOR.90, .92, ..., for "beta" (test) releases, and .91, .93, ... for "alpha" (development). Follows the 2024-01-21 change. * HACKING: typo en passant.