fixed deprecated version of vim.validate()

[pebbe]

Description

The use of vim.validate(spec) is deprecated.

Type of change

Changed all calls to vim.validate(spec) into calls to vim.validate(name, value, validator[, optional][, message])

Configuration:

• Neovim version (nvim --version): v0.11.2
• Operating system and version: Debian GNU/Linux bookworm 12.11 x86_64

Checklist:

• [x] My code follows the style guidelines of this project (stylua)
• [ ] I have performed a self-review of my own code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation (lua annotations)