[BUG] 3002.6 pkgrepo.managed creates multiple identical lines in sources.list.d file for Ubuntu

Description

pkgrepo.managed:
  - name: {{ repostring }}
  - file: /etc/apt/sources.list.d/foo.list
  - key_url: {{ keyurl }}

This code in a state sls file causes the same line to be repeated in /etc/apt/sources.list.d/*.list:

deb http://repositories.tools/platforms/mo bionic main
deb http://repositories.tools/platforms/mo bionic main
deb http://repositories.tools/platforms/mo bionic main
deb http://repositories.tools/platforms/mo bionic main
deb http://repositories.tools/platforms/mo bionic main
deb http://repositories.tools/platforms/mo bionic main
deb http://repositories.tools/platforms/mo bionic main

Every state.apply adds a new identical line.

Setup

# cat foo/init.sls
{% from "foo/map.jinja" import foo with context %}

foo.repo:
  pkgrepo.managed:
    - name: {{ foo.repostring }}
    - file: /etc/apt/sources.list.d/foo.list
    - key_url: {{ foo.keyurl }}


# cat foo/map.jinja
{% set foo = salt['grains.filter_by']({
    'xenial': {
        'repostring': 'deb http://repositories.tools/platforms/mo xenial main',
        'keyurl': 'http://repositories.tools/keys/foo.gpg',
        'pkg': 'foo',
        'version': '11.1'
    },
    'bionic': {
        'repostring': 'deb http://repositories.tools/platforms/mo bionic main',
        'keyurl': 'http://repositories.tools/platforms/all/all.key',
        'pkg': 'foo',
        'version': '11.2'
    },
    'focal': {
        'repostring': 'deb http://repositories.tools/platforms/mo focal main',
        'keyurl': 'http://repositories.tools/platforms/all/all.key',
        'pkg': 'foo',
        'version': '11.3'
    },
}, grain='oscodename') %}

Steps to Reproduce the behavior

# salt-call state.apply

every state.apply adds a new identical line to the sources.list.d file

Expected behavior
Only one line of the same kind in the sources.list.d file.

Versions Report

# salt --versions-report
Salt Version:
          Salt: 3002.6

Dependency Versions:
          cffi: Not Installed
      cherrypy: unknown
      dateutil: 2.7.3
     docker-py: Not Installed
         gitdb: Not Installed
     gitpython: Not Installed
        Jinja2: 2.10.1
       libgit2: 0.28.3
      M2Crypto: Not Installed
          Mako: Not Installed
       msgpack: 0.6.2
  msgpack-pure: Not Installed
  mysql-python: Not Installed
     pycparser: Not Installed
      pycrypto: 2.6.1
  pycryptodome: 3.6.1
        pygit2: 1.0.3
        Python: 3.8.5 (default, Jan 27 2021, 15:41:15)
  python-gnupg: 0.4.5
        PyYAML: 5.3.1
         PyZMQ: 18.1.1
         smmap: Not Installed
       timelib: Not Installed
       Tornado: 4.5.3
           ZMQ: 4.3.2

System Versions:
          dist: ubuntu 20.04 focal
        locale: utf-8
       machine: x86_64
       release: 5.4.0-66-generic
        system: Linux
       version: Ubuntu 20.04 focal
</details>

**Additional context**
Add any other context about the problem here.

Start by reproducing the issue with the shown pkgrepo.managed state and repeated state.apply commands, inspecting /etc/apt/sources.list.d/foo.list after each run. Trace the pkgrepo.managed entry point and its handling of the file option. Done means repeated applies leave only one identical repository line in the sources.list.d file.