tests: skip to_excel test if pyexcel is not installed
tests: skip to_excel test if pyexcel is not installed

yagebu/fava,aumayr/beancount-web,aumayr/beancount-web,beancount/fava,beancount/fava,yagebu/fava,beancount/fava,aumayr/beancount-web,beancount/fava,yagebu/fava,yagebu/fava,beancount/fava,yagebu/fava,aumayr/beancount-web