1.20.1 (2026-09-12)

• Update wheels to libgit2 1.9.7

• New exception hierarchy: AlreadyExistsError, InvalidSpecError,
  InvalidError, NotFoundError, AmbiguousError, AuthError, and
  CertificateError all inherit from GitError and the appropriate Python
  built-in exception (ValueError/KeyError) for backward compatibility
  #830

• Fix DiffDelta.is_binary and DiffDelta.flags returning stale values for
  deltas obtained from Diff.deltas; flags are now loaded lazily
  #962
  #1100

• Fix repo.submodules.get() and name in repo.submodules raising
  AlreadyExistsError when a repository exists at the submodule path but was
  never registered as a submodule; they now return None and False
  respectively as documented
  #1487

• Fix BlobIO cleanup deadlock on partial reads
  #1488
  #1491

• Fix leaks and crashes in error paths
  #1478
  #1479
  #1480
  #1481

• Fix custom ODB and refdb backend callbacks overwriting a pending Python
  exception (e.g. RuntimeError) with a stale libgit2 error message.

• Documentation fixes
  #1490

• CI (macOS): build architecture-specific OpenSSL/libssh2/libgit2
  dependencies instead of universal binaries, producing smaller wheels.