GARDNER — The sound of music will be returning to Monument Park — and one surprise location — this summer. Officials announced that the 2021 Gardner Summer Concert Series, which was canceled last year due to the pandemic, will kick off with the classic rock sounds of Danny LeBlanc on Saturday, June 19. But organizers admit that they were not entirely certain what the pandemic situation would be when they first starting scheduling possible shows at the beginning of the year. “We began booking bands via Zoom meetings starting in January so that if we got the OK (to hold the concerts), we’d be ready to go,” said Michael Zlotnik, chairman of the city’s Bandstand Committee. “The bands were all very cooperative and understood that things could change at the last minute.”