cmd/viewer,all: consistently use "read-only" instead of "readonly"

Updates #cleanup

Change-Id: I8e4e3497d3d0ec5b16a73aedda500fe5cfa37a67
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This commit is contained in:
Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f