1.21.0 (2026-11-04)

• Add support for Python 3.15
  #1498

• New Config subclasses: DefaultConfig for the default configuration and
  RepositoryConfig for repository configurations
  #1501

• Fix ConfigEntry retaining git_config_entry pointers owned by config
  iterators, which could make entry values change unexpectedly and cause
  crashes; values are now copied eagerly
  #1499

• Fix custom ODB backends: acquire the GIL when calling back into Python,
  and fix write_cb's type argument
  #1496

• Fix References.get(), Branches.get(), and the in operator on both
  collections raising InvalidSpecError for invalid names; they now return
  None and False respectively, as documented
  #1495

• Fix sh build.sh stubtest
  #1492

• Wheels: Build the bundled libgit2 and libssh2 in Release mode instead of Debug
  #1497

• Wheels: Update OpenSSL to 3.5.9
  #1506