Fix two regressions in :mod:`dataclasses` in Python 3.14.1 related to
annotations.

* An exception is no longer raised if ``slots=True`` is used and the
  ``__init__`` method does not have an ``__annotate__`` attribute
  (likely because ``init=False`` was used).

* An exception is no longer raised if annotations are requested on the
  ``__init__`` method and one of the fields is not present in the class
  annotations. This can occur in certain dynamic scenarios.

Patch by Jelle Zijlstra.
