Allow '%' in config file values

ConfigParser interpolation treats '%' as special, so a path or
pattern containing it crashed the program. Disable interpolation,
which is not used by the config file.

simple_backup/simple_backup.py

@@ -750,7 +750,8 @@ def _read_config(config_file, user: Optional[str] = None):
 
         return config_args
 
-    config = configparser.ConfigParser()
+    # Disable interpolation, so that '%' can be used in paths and patterns
+    config = configparser.ConfigParser(interpolation=None)
     config.read(config_file)
 
     section = 'backup'