fix bug in sending member meeting notification to Telegram on html format/syntax errors

pythnanywhere server log entries for unsent member meeting notification errors on all 3 languages (en, es and de):

• 2024-06-02 14:26:22 *** send_chg_notif() error with message 'Member Meeting notification (by 2)
  
  

  #015#012Dear Kairosians,#015#012we're taking a summer break until September. Take care until then.' to 'telegram:-1001156056653=Kairos-Telegram-Group': error sending 'to_html' Telegram message to 'Kairos-Telegram-Group': {'ok': False, 'error_code': 400, 'description': 'Bad Request: can't parse entities: Can't find end tag corresponding to start tag "b"'}

• 2024-06-02 14:26:24 *** send_chg_notif() error with message 'Notificación de Reunion de Miembros (por 2)
  
  

  #015#012Queridos Kairosianos,#015#012nos tomaremos unas vacaciones de verano hasta septiembre. Te he tenido hasta entonces.' to 'telegram:-1001156056653=Kairos-Telegram-Group': error sending 'to_html' Telegram message to 'Kairos-Telegram-Group': {'ok': False, 'error_code': 400, 'description': 'Bad Request: can't parse entities: Can't find end tag corresponding to start tag "b"'}

• 2024-06-02 14:26:25 *** send_chg_notif() error with message 'Mitglieder-Treffen-Benachrichtigung (von 2)
  
  

  #015#012Liebe Kairosianer,#015#012wir machen Sommerpause bis zum September. Gehabt euch wohl bis dahin.' to 'telegram:-1001156056653=Kairos-Telegram-Group': error sending 'to_html' Telegram message to 'Kairos-Telegram-Group': {'ok': False, 'error_code': 400, 'description': 'Bad Request: can't parse entities: Can't find end tag corresponding to start tag "b"'}