dynamic:instance-identity:document grain is not parsed on Debian 10 Buster

Description
dynamic:instance-identity:document grain is not parsed on Debian 10 Buster. It is a JSON value instead of being parsed.

Comparison of two EC2 instances:

sudo salt --out=yaml c\*__stage__\* grains.item osfinger pythonexecutable dynamic:instance-identity:document

chapters__stage__us-east-2:
  dynamic:instance-identity:document:
    accountId: '[REDACTED]'
    architecture: x86_64
    availabilityZone: us-east-2a
    billingProducts: null
    devpayProductCodes: null
    imageId: ami-0b8193ae73862dccd
    instanceId: i-004930517fd5e82cc
    instanceType: t3.medium
    kernelId: null
    marketplaceProductCodes: null
    pendingTime: '2019-03-29T15:00:23Z'
    privateIp: 10.22.10.18
    ramdiskId: null
    region: us-east-2
    version: '2017-09-30'
  osfinger: Debian-9
  pythonexecutable: /usr/bin/python2
ccengine__stage__us-east-2:
  dynamic:instance-identity:document: "{\n  \"accountId\" : \"[REDACTED]\",\n  \"architecture\"
    : \"x86_64\",\n  \"availabilityZone\" : \"us-east-2b\",\n  \"billingProducts\"
    : null,\n  \"devpayProductCodes\" : null,\n  \"marketplaceProductCodes\" : null,\n
    \ \"imageId\" : \"ami-05d9978d11a05da49\",\n  \"instanceId\" : \"i-0629d310e88d71c31\",\n
    \ \"instanceType\" : \"t3.small\",\n  \"kernelId\" : null,\n  \"pendingTime\"
    : \"2020-04-24T15:45:14Z\",\n  \"privateIp\" : \"10.22.11.12\",\n  \"ramdiskId\"
    : null,\n  \"region\" : \"us-east-2\",\n  \"version\" : \"2017-09-30\"\n}"
  osfinger: Debian-10
  pythonexecutable: /usr/bin/python3

Expected behavior
The individual document values should be accessible (ex. dynamic:instance-identity:document:region).

Versions Report

Salt Version:
           Salt: 2019.2.3
 
Dependency Versions:
           cffi: Not Installed
       cherrypy: Not Installed
       dateutil: 2.5.3
      docker-py: Not Installed
          gitdb: 2.0.0
      gitpython: 2.1.1
          ioflo: Not Installed
         Jinja2: 2.9.4
        libgit2: 0.24.5
        libnacl: Not Installed
       M2Crypto: Not Installed
           Mako: Not Installed
   msgpack-pure: Not Installed
 msgpack-python: 0.4.8
   mysql-python: Not Installed
      pycparser: Not Installed
       pycrypto: 2.6.1
   pycryptodome: Not Installed
         pygit2: 0.24.2
         Python: 2.7.13 (default, Sep 26 2018, 18:42:22)
   python-gnupg: Not Installed
         PyYAML: 3.12
          PyZMQ: 16.0.2
           RAET: Not Installed
          smmap: 2.0.1
        timelib: Not Installed
        Tornado: 4.4.3
            ZMQ: 4.2.1
 
System Versions:
           dist: debian 9.12 
         locale: UTF-8
        machine: x86_64
        release: 4.9.0-12-amd64
         system: Linux
        version: debian 9.12

Additional context
The State and Pillar files are publicly accessible (secrets are encrypted): creativecommons/sre-salt-prime

No source file or test is named in the issue. Trace Salt's grain parsing entry point for dynamic:instance-identity:document and compare the Debian 9 and Debian 10 behavior; done means nested values such as dynamic:instance-identity:document:region are accessible instead of remaining a JSON string.