fix(sql): only use cmp if it is available (#4891)

## Description

The blink and sql extras are currently conflicting because the sql extra
has a hard dependency on nvim-cmp, which is disabled by the blink extra.
Introducing a check for cmp in the sql extra resolves this.

## Checklist

- [x] I've read the
[CONTRIBUTING](https://github.com/LazyVim/LazyVim/blob/main/CONTRIBUTING.md)
guidelines.

Co-authored-by: Jakob Pfender <jakob.pfender@safetyio.com>

lua/lazyvim/plugins/extras/lang/sql.lua

@@ -48,6 +48,7 @@ return {
       vim.api.nvim_create_autocmd("FileType", {
         pattern = sql_ft,
         callback = function()
+          if LazyVim.has("cmp") then
             local cmp = require("cmp")
 
             -- global sources
@@ -61,6 +62,7 @@ return {
 
             -- update sources for the current buffer
             cmp.setup.buffer({ sources = sources })
+          end
         end,
       })
     end,