use f-strings in module utils (#10901)

* use f-strings in module utils

* Apply suggestions from code review

Co-authored-by: Felix Fontein <felix@fontein.de>

* remove unused imports

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Co-authored-by: Felix Fontein <felix@fontein.de>

plugins/module_utils/ssh.py

@@ -13,7 +13,7 @@ import os
 
 def determine_config_file(user, config_file):
     if user:
-        config_file = os.path.join(os.path.expanduser('~%s' % user), '.ssh', 'config')
+        config_file = os.path.join(os.path.expanduser(f'~{user}'), '.ssh', 'config')
     elif config_file is None:
         config_file = '/etc/ssh/ssh_config'
     return config_file