Bump nginx from 1.15.10-alpine to 1.21.1-alpine in /1.2.1/nginx-mainline/alpine#29

dependabot-preview[bot] wants to merge 1 commit intomasterLCMApps/docker-nginx-rtmp:masterfrom

dependabot/docker/1.2.1/nginx-mainline/alpine/nginx-1.21.1-alpineLCMApps/docker-nginx-rtmp:dependabot/docker/1.2.1/nginx-mainline/alpine/nginx-1.21.1-alpineCopy head branch name to clipboard