diskann-benchmark\example\flat-index.json uses graph ground truth which is not equal #1172

cargo run --package diskann-benchmark --release -- run --input-file ./diskann-benchmark/example/flat-index.json --output-file ./target/tmp/flat-index-output.json                           
    Finished `release` profile [optimized + debuginfo] target(s) in 8.83s
     Running `target\release\diskann-benchmark.exe run --input-file ./diskann-benchmark/example/flat-index.json --output-file ./target/tmp/flat-index-output.json`
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# Running Job 1 of 1 #
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              Data: test_data/disk_index_search\disk_index_siftsmall_learn_256pts_data.fbin
         Data Type: float32
          Distance: squared_l2
           Queries: test_data/disk_index_search\disk_index_sample_query_10pts.fbin
       Groundtruth: test_data/disk_index_search\disk_index_10pts_idx_uint32_truth_search_res.bin
                 K: 10
           Threads: 1
              Reps: 1

Loading dataset...
  Loaded 256 vectors of dimension 128
  Queries: 10, Groundtruth: 10x10


 K,   Avg cmps,   QPS - mean(max),       Avg Latency,     p99 Latency,               Recall,   Threads
======================================================================================================
10,        256,   7745.9 (7745.9),   15.0us (15.0us),   79.0us (79us),   0.9099999999999999,         1