fix(diagnostic): get border from config (#28531)

Co-authored-by: Justin M. Keyes <justinkz@gmail.com>
Co-authored-by: Gregory Anders <greg@gpanders.com>

runtime/lua/vim/_defaults.lua

@@ -190,7 +190,7 @@ do
     })
 
     vim.keymap.set('n', '<C-W>d', function()
-      vim.diagnostic.open_float({ border = 'rounded' })
+      vim.diagnostic.open_float()
     end, {
       desc = 'Open a floating window showing diagnostics under the cursor',
     })