Merge branch 'ms/reftable-block-writer-errors'

Give more meaningful error return values from block writer layer of the reftable ref-API backend. * ms/reftable-block-writer-errors: reftable: adapt write_object_record() to propagate block_writer_add() errors reftable: adapt writer_add_record() to propagate block_writer_add() errors reftable: propagate specific error codes in block_writer_add()