So, who died and made you Pope?
It may or may not be a sin, I seriously doubt its a mortal sin. I do not see any reference in Canon law to it being a grave sin.
I can name an awful lot of REALLY faithful priests who would be in hot water according to this article. Several who even wear shorts when they run and lift weights. Jeans when putting up pipe and drape for official occasions. In an official capacity, these men are always in clerical garb, but when practicality calls for something in which to get dirty, now that’s something else.