Respect to those who would, but not for me and I'm fairly sure neither of my bands would either.
The purpose of being asked to play in these circumstances would surely be to increase the takings at the venue, presumably to a level where they not only cover their costs, but make some money out of it - but none goes to the band? Given that pubs can open (within restrictive guidelines) and the only way most bands can play at a pub is if the venue has the facility for outside performance, I find the 'for free' thing a little difficult to comprehend at the moment.