Switch to <C-l> to confirm completions

Previous mapping of <C-y> caused issues due to y being too close to u so
fat fingers would immediately undo the completion expansion.

lua/plugins/completions.lua

@@ -75,7 +75,7 @@ return {
       mapping = cmp.mapping.preset.insert({
         ['<C-p>'] = cmp.mapping.select_prev_item(),
         ['<C-n>'] = cmp.mapping.select_next_item(),
-        ['<C-y>'] = cmp.mapping.confirm({ select = true }),
+        ['<C-l>'] = cmp.mapping.confirm({ select = true }),
       }),
       sources = {
         { name = 'nvim_lsp' },