fix(pypi): update dependency pygit2 to v1.20.0

[renovate]

This PR contains the following updates:

Package	Change	Age	Confidence
pygit2 (changelog)	==1.19.3 → ==1.20.0

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Release Notes

libgit2/pygit2 (pygit2)

v1.20.0

Compare Source

• New RemoteCallbacks.custom_headers()
  #​1465

• New rebase API: Repository.rebase_init(...), Repository.rebase_open(...),
  Rebase, and RebaseOperation
  #​1483

• Fix Config.snapshot() for non-repository configs, allow PathLike in
  Config.__init__(), and improve config documentation
  #​1468

• Fix UnicodeDecodeError with non-UTF-8 file paths in Repository.status(),
  DiffFile.path, index paths, checkout callbacks, and related APIs
  #​1451
  #​1469

• Fix enums.CheckoutStrategy.CONFLICT_STYLE_ZDIFF3, which was mistakenly
  bound to the DIFF3 constant
  #​1483

• Fix crashes and reference-lifetime bugs in custom refdb backends
  #​1471
  #​1474
  #​1475
  #​1476

• Update wheels to libgit2 1.9.6 and OpenSSL 3.5.7

• Add riscv64 wheels
  #​1463

Breaking changes:

• Remove deprecated pygit2.legacyenums module and GIT_* constants,
  use pygit2.enums instead

• Remove deprecated support for passing str to Repository.merge(...),
  pass a Commit, Oid, or Reference object instead

• Repository.merge_file_from_index(...) now returns MergeFileResult by
  default; pass use_deprecated=True for the previous string return, now
  deprecated.

• Remove deprecated Remote.ls_remotes(...), use Remote.list_heads(...)
  instead

• Remove pygit2.to_bytes(...) and pygit2.to_str(...); they were undocumented
  accidental public APIs

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