[BUG] key_cache: sched throws exceptions on 3007.x as pki_dir is not accessible from the function

[akrus]

Description
When key_cache: sched is enabled in the configuration, Salt Master process throws unhandled exception in the logs every 10 seconds:

2025-01-22 08:19:16,192 [salt.utils.process:1000][ERROR   ][40178] An un-handled exception from the multiprocessing process 'Maintenance' was caught:
Traceback (most recent call last):
  File "/opt/saltstack/salt/lib/python3.10/site-packages/salt/utils/process.py", line 995, in wrapped_run_func
    return run_func()
  File "/opt/saltstack/salt/lib/python3.10/site-packages/salt/master.py", line 312, in run
    self.handle_key_cache()
  File "/opt/saltstack/salt/lib/python3.10/site-packages/salt/master.py", line 339, in handle_key_cache
    os.path.join(self.pki_dir, acc, ".key_cache"), mode="wb"
AttributeError: 'Maintenance' object has no attribute 'pki_dir'

Setup
Nothing is needed in particular, simply specify key_cache: sched.

Steps to Reproduce the behavior
key_cache: sched in the configuration.

Expected behavior
key_cache is expected to work.

Screenshots
If applicable, add screenshots to help explain your problem.

Versions Report

salt --versions-report

(Provided by running salt --versions-report. Please also mention any differences in master/minion versions.)

Salt Version:
          Salt: 3007.1

Python Version:
        Python: 3.10.14 (main, Apr  3 2024, 21:30:09) [GCC 11.2.0]

Dependency Versions:
          cffi: 1.17.1
      cherrypy: unknown
      dateutil: 2.8.2
     docker-py: Not Installed
         gitdb: Not Installed
     gitpython: Not Installed
        Jinja2: 3.1.4
       libgit2: 1.9.0
  looseversion: 1.3.0
      M2Crypto: Not Installed
          Mako: Not Installed
       msgpack: 1.0.7
  msgpack-pure: Not Installed
  mysql-python: Not Installed
     packaging: 23.1
     pycparser: 2.21
      pycrypto: Not Installed
  pycryptodome: 3.19.1
        pygit2: 1.17.0
  python-gnupg: 0.5.2
        PyYAML: 6.0.1
         PyZMQ: 25.1.2
        relenv: 0.16.0
         smmap: Not Installed
       timelib: 0.3.0
       Tornado: 6.3.3
           ZMQ: 4.3.4

Salt Package Information:
  Package Type: onedir

System Versions:
          dist: ubuntu 22.04.5 jammy
        locale: utf-8
       machine: x86_64
       release: 5.15.0-130-generic
        system: Linux
       version: Ubuntu 22.04.5 jammy

Additional context
Adding

self.pki_dir = self.opts["pki_dir"]

to salt/master.py around line 333 fixes the issue, but as it's probably needed for a clustered setup, more work needs to be done.

This was introduced with the commit:
8764aa9
(@dwoz probably can help)