Description of problem:

python3-dnf:
If the vars directory happens to have a non-file, the var val is not set
and an uncaught Exception is triggered


Version-Release number of selected component (if applicable):
4.10.0-5.el9_0

How reproducible:
Depends on how python parses the varsdir

Steps to Reproduce:
1. In the dnf varsdir add random non-files (like links)
2.
3.

Actual results:
Traceback (most recent call last):
  File "/bin/reposync", line 101, in <module>
    main.user_main(MAPPING[command] + args, exit_code=True)
  File "/usr/lib/python3.9/site-packages/dnf/cli/main.py", line 201, in user_main
    errcode = main(args)
  File "/usr/lib/python3.9/site-packages/dnf/cli/main.py", line 67, in main
    return _main(base, args, cli_class, option_parser_class)
  File "/usr/lib/python3.9/site-packages/dnf/cli/main.py", line 102, in _main
    cli.configure(list(map(ucd, args)), option_parser())
  File "/usr/lib/python3.9/site-packages/dnf/cli/cli.py", line 799, in configure
    self._read_conf_file(opts.releasever)
  File "/usr/lib/python3.9/site-packages/dnf/cli/cli.py", line 933, in _read_conf_file
    subst.update_from_etc(from_root, varsdir=conf._get_value('varsdir'))
  File "/usr/lib/python3.9/site-packages/dnf/conf/substitutions.py", line 64, in update_from_etc
    self[fsvar] = val
UnboundLocalError: local variable 'val' referenced before assignment



Expected results:
Non-files are ignored

Additional info:

The indentation level at line 64 looks wrong perhaps?
     44     def update_from_etc(self, installroot, varsdir=("/etc/yum/vars/", "/etc/dnf/vars/")):
     45         # :api
     46 
     47         for vars_path in varsdir:
     48             fsvars = []
     49             try:
     50                 dir_fsvars = os.path.join(installroot, vars_path.lstrip('/'))
     51                 fsvars = os.listdir(dir_fsvars)
     52             except OSError:
     53                 continue
     54             for fsvar in fsvars:
     55                 filepath = os.path.join(dir_fsvars, fsvar)
     56                 if os.path.isfile(filepath):
     57                     try:
     58                         with open(filepath) as fp:
     59                             val = fp.readline()
     60                         if val and val[-1] == '\n':
     61                             val = val[:-1]
     62                     except (OSError, IOError) as exc:
     63                         continue
     64                 self[fsvar] = val