wlroots 0.20.0-rc3

Isaac Freund (1):
      backend/x11: reject shm buffers with non-min strides

Kenny Levinsen (1):
      backend/drm: Close non-master drm fd on failure

Simon Ser (2):
      backend/libinput: guard against new enum entries
      build: bump version to 0.20.0-rc3

hrdl (1):
      CONTRIBUTING.md: update git host