bug: Util.is_dark resolves incorrectly.

[mehalter]

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• I have read all the todo-comments.nvim docs
• I have updated the plugin to the latest version before submitting this issue
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• I have searched the existing issues of plugins related to this issue

Neovim version (nvim -v)

0.10.1

Operating system/version

Arch Linux

Describe the bug

Util.is_dark is not resolving correctly in some edge cases it looks like which results in some colorschemes having unreadable todo notes.

#00B298 is an example of a color that results in true in is_dark and gets a light foreground which is unreadable

Steps To Reproduce

1. Set DiagnosticHint fg to #00B298
2. Make a NOTE highlight
3. See that the text is unreadable

Expected Behavior

The text should get the dark foreground color which makes it readable

Repro

vim.env.LAZY_STDPATH = ".repro"
load(vim.fn.system("curl -s https://raw.githubusercontent.com/folke/lazy.nvim/main/bootstrap.lua"))()

require("lazy.minit").repro({
  spec = {
    {
      "folke/todo-comments.nvim",
      dependencies = { { "nvim-lua/plenary.nvim", lazy = true } },
      opts = {},
    },
    {
      "folke/tokyonight.nvim",
      opts = {
        on_highlights = function(hl)
          hl.DiagnosticHint = { fg = "#00B298" }
        end,
      },
    },
  },
})