bump Giraffe dependency to 6.4

[et1975]

This PR fixes #380

Tested by referencing my local build of Saturn instead of the nuget package.

[baronfel]

Paket Lock Diff Report

This report was generated via Paket Lock Diff

Additions - (0)

Removals - (1)

• Main - (1)
  • Utf8Json - 1.3.7

Version Upgrades - (5)

• Main - (5)
  • Minor - (1)
    • Giraffe - 6.0.0 -> 6.4.0
  • Major - (3)
    • Microsoft.IO.RecyclableMemoryStream - 2.2.0 -> 3.0.0
    • System.Text.Encodings.Web - 6.0.0 -> 8.0.0
    • System.Text.Json - 6.0.2 -> 8.0.3
  • Patch - (1)
    • Newtonsoft.Json - 13.0.1 -> 13.0.3

Version Downgrades - (0)

[baronfel]

This LGTM overall - I was trying to get a Fuget-based API diff of the changes in Giraffe from 6.0 to 6.4 but the site keeps crashing.