nix: Fix source filtering on latency benchmark

[rvl]

The latency benchmark needs test data files, but they were getting removed by haskell-nix.haskellSourceFilter.

Comments

Tested with:

nix build .#benchmarks.cardano-wallet.latency && ./result/bin/latency

Issue Number

ADP-1444

[piotr-iohk]

It works!

$ ./.buildkite/bench-latency.sh
--- Build
+++ Run benchmark - shelley
...
        getNetworkInfo      - 26.1 ms
    Latencies for 2 fixture wallets scenario
        listWallets         - 1.8 ms
        getWallet           - 0.5 ms
        getUTxOsStatistics  - 0.4 ms
...