[BUG] Permission denied: '/etc/salt/minion.d/mine.conf'

Description
I upgraded an old salt-master from Debian 9 to Debian 11. salt-master is now failing to start which I believe is caused by a change https://bugs.debian.org/891303 (Change salt master user from 'root' to 'salt' by default). /var/log/salt/master contains:

2022-08-04 16:18:09,119 [salt.utils.process:900 ][ERROR   ][2651] An un-handled exception from the multiprocessing process 'MWorker-3' was caught:
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/salt/utils/process.py", line 895, in wrapped_run_func
    return run_func()
  File "/usr/lib/python3/dist-packages/salt/master.py", line 1237, in run
    self.clear_funcs = ClearFuncs(self.opts, self.key,)
  File "/usr/lib/python3/dist-packages/salt/master.py", line 2068, in __init__
    self.mminion = salt.minion.MasterMinion(
  File "/usr/lib/python3/dist-packages/salt/minion.py", line 981, in __init__
    self.opts = salt.config.minion_config(
  File "/usr/lib/python3/dist-packages/salt/config/__init__.py", line 2186, in minion_config
    include_config(
  File "/usr/lib/python3/dist-packages/salt/config/__init__.py", line 2065, in include_config
    opts = _read_conf_file(fn_)
  File "/usr/lib/python3/dist-packages/salt/config/__init__.py", line 1902, in _read_conf_file
    with salt.utils.files.fopen(path, "r") as conf_file:
  File "/usr/lib/python3/dist-packages/salt/utils/files.py", line 396, in fopen
    f_handle = open(*args, **kwargs)  # pylint: disable=resource-leakage
PermissionError: [Errno 13] Permission denied: '/etc/salt/minion.d/mine.conf'

I am wondering about this, thought this was resolved via #29831 / #30068.

Steps to Reproduce the behavior
Should be enough to create a permission chain like

# ls -ld /etc/salt
drwxr-xr-x 5 root root 94 Aug  4 15:53 /etc/salt
# ls -ld /etc/salt/minion.d/
drwxr-xr-x 2 root root 45 Mar 21  2017 /etc/salt/minion.d/
# ls -l /etc/salt/minion.d/mine.conf
-rw-r----- 1 root root 17 Mar 21  2017 /etc/salt/minion.d/mine.conf

Expected behavior
According to the linked two issues, minion config shouldn't cause such troubles for salt-master.

Also, salt-master shouldn't consume 100% CPU when running into this...

# ps faux | grep salt-ma
salt         892  0.4  0.3  74280 60084 ?        Ss   16:17   0:02 /usr/bin/python3 /usr/bin/salt-master
salt        1143  0.0  0.0      0     0 ?        Z    16:17   0:00  \_ [salt-master] <defunct>
salt        1871  0.0  0.3 155852 52512 ?        Sl   16:17   0:00  \_ /usr/bin/python3 /usr/bin/salt-master
salt        1872  0.0  0.3  73944 49104 ?        S    16:17   0:00  \_ /usr/bin/python3 /usr/bin/salt-master
salt        1882  0.0  0.3  74400 49348 ?        S    16:17   0:00  \_ /usr/bin/python3 /usr/bin/salt-master
salt        1883  100  0.3 450840 53360 ?        Rl   16:17   8:13  |   \_ /usr/bin/python3 /usr/bin/salt-master
salt        2649  0.0  0.0      0     0 ?        Z    16:18   0:00  |   \_ [salt-master] <defunct>
salt        1895  0.0  0.2 147992 48804 ?        Sl   16:17   0:00  \_ /usr/bin/python3 /usr/bin/salt-master
salt        2765  0.0  0.0      0     0 ?        Z    16:19   0:00  \_ [salt-master] <defunct>
root        3038  0.0  0.0   7892   712 pts/1    S+   16:26   0:00      \_ grep --colour=auto salt-ma

Versions Report

# salt-master --versions-report                                                                                                    [1/39]
Salt Version:
          Salt: 3002.6

Dependency Versions:
          cffi: Not Installed
      cherrypy: Not Installed
      dateutil: 2.8.1
     docker-py: Not Installed
         gitdb: Not Installed
     gitpython: Not Installed
        Jinja2: 2.11.3
       libgit2: Not Installed
      M2Crypto: Not Installed
          Mako: Not Installed
       msgpack: 1.0.0
  msgpack-pure: Not Installed
  mysql-python: Not Installed
     pycparser: Not Installed
      pycrypto: Not Installed
  pycryptodome: 3.9.7
        pygit2: Not Installed
        Python: 3.9.2 (default, Feb 28 2021, 17:03:44)
  python-gnupg: Not Installed
        PyYAML: 5.3.1
         PyZMQ: 20.0.0
         smmap: Not Installed
       timelib: Not Installed
       Tornado: 4.5.3
           ZMQ: 4.3.4

System Versions:
          dist: debian 11 bullseye
        locale: utf-8
       machine: x86_64
       release: 5.10.0-16-amd64
        system: Linux
       version: Debian GNU/Linux 11 bullseye

Additional context
Already started with Debian 10, i.e. upgrade salt-master:all 2016.11.2+ds-1+deb9u10 -> 2018.3.4+dfsg1-6+deb10u3

Start with the traceback paths in salt/config/init.py and salt/master.py, then inspect the process handling in salt/utils/process.py and file access in salt/utils/files.py. Reproduce the unreadable /etc/salt/minion.d/mine.conf case and verify that salt-master handles the permission error without failing to start or consuming 100% CPU.