THIS OPTION IS EXPERIMENTAL! SHA-256 support is experimental and still
in an early stage.  A SHA-256 repository will in general not be able to
share work with "regular" SHA-1 repositories.  It should be assumed
that, e.g., Git internal file formats in relation to SHA-256
repositories may change in backwards-incompatible ways.  Only use
`--object-format=sha256` for testing purposes.