persistent-template does not package up benchmark files

persistent-template currently does not package up the benchmark files as part of its Hackage release.

This manifests in the following failure when trying to run the benchmarks from the release package:

    /var/stackage/work/unpack-dir/unpacked/persistent-template-2.7.2-dd4aa468a9b26d3c0f64
261d0a238ff6b9adf9b4889e112709826a23b6abfd8d/bench/Main.hs:20:49: error:
        • Exception when trying to run compile-time code:
            bench/models-slowly: openFile: does not exist (No such file or directory)
          Code: persistFileWith lowerCaseSettings "bench/models-slowly"
        • In the untyped splice:
            $(persistFileWith lowerCaseSettings "bench/models-slowly")
       |
    20 |         [ bench "From File" $ nfIO $ mkPersist' $(persistFileWith lowerCaseSetti
ngs "bench/models-slowly")
       |                                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
^^^^^^^^^^^^^^^^^^^^^^^^^^

I believe the relevant line to add this is here.