Beet failed to deserialize some JSON files when the build process needs to fetch objects.

Minimal Reproducible Example

# beet.yml
meta:
  vanilla:
    version: "1.21.8"

pipeline:
  - mre

# mre.py
from beet import Context
from beet.contrib.vanilla import Vanilla

def beet_default(ctx: Context):
  ctx.inject(Vanilla).mount("assets/minecraft/font", fetch_objects=True)

Steps:

1. Run beet cache --clear to clear the cache
2. Run beet build
   ❌ - Couldn't deserialize object 402ded0eebd448033ef415e861a17513075f80e7 in the cache folder
   json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)
3. Run beet build again
   ✅ - Build completed