The internal trade union representing staff at Venice's La Fenice opera house on Wednesday called a strike for Friday October 17, the date of the premiere of Berg's Wozzeck, against the recent appointment of conductor Beatrice Venezi as new musical director of the storied theatre.     Venezi, 35, was appointed government musical advisor by Premier Giorgia Meloni shortly after she came to power three years ago and she has been praised by the premier on several occasions, also receiving an award