[app] improvement: adding the environment variable if not available

CHANGELOG.md

@@ -16,6 +16,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
     - custom themes: `/usr/share/bauh/themes`
     - symlinks/binaries : `/usr/local/bin`
     - shared files: `/usr/local/share/bauh`
+  - adding the `XDG_RUNTIME_DIR` environment variable if not available (following the pattern `/run/user/$UID`)
 
 - UI 
   - settings panel: 

bauh/app.py

@@ -15,6 +15,9 @@ def main(tray: bool = False):
     if not os.getenv('PYTHONUNBUFFERED'):
         os.environ['PYTHONUNBUFFERED'] = '1'
 
+    if not os.getenv('XDG_RUNTIME_DIR'):
+        os.environ['XDG_RUNTIME_DIR'] = f'/run/user/{os.getuid()}'
+
     faulthandler.enable()
     urllib3.disable_warnings(urllib3.exceptions.InsecureRequestWarning)