cannot `pairs` on a table that uses enum values for keys

```lua
--- @enum Severity
local severity = {
  ERROR = 1,
  WARN = 2,
  INFO = 3,
  HINT = 4,
}

local severities = {
  [severity.ERROR] = 1,
  [severity.WARN] = 2,
  [severity.INFO] = 3,
  [severity.HINT] = 4,
}

for k in pairs(severities) do
  local _ = k -- k is unknown
end
```