nvim: colors/yolokai: Disable under curl for diagnostics

While we like having undercurl for diagnostics, most code bases are
garbage and linters/LSP show warnings all over the place. Seeing the
screen filled with red undercurls feels jarring. Disable them. Can't
expect people to do things properly.

nvim/.config/nvim/colors/yolokai.vim

@@ -194,10 +194,10 @@ local highlight_groups = {
 	DiagnosticSignInformation        = 'InfoMsg'          ,
 	DiagnosticSignHint               = 'HintMsg'          ,
 
-	DiagnosticUnderlineError         = {style={'undercurl', color=red    }},
-	DiagnosticUnderlineWarning       = {style={'undercurl', color=pink   }},
-	DiagnosticUnderlineInformation   = {style={'undercurl', color=orange }},
-	DiagnosticUnderlineHint          = {style={'undercurl', color=purple }},
+	DiagnosticUnderlineError         = 'ErrorMsg'         ,
+	DiagnosticUnderlineWarning       = 'WarningMsg'       ,
+	DiagnosticUnderlineInformation   = 'InfoMsg'          ,
+	DiagnosticUnderlineHint          = 'HintMsg'          ,
 
 	DiagnosticVirtualTextError       = 'ErrorMsg'         ,
 	DiagnosticVirtualTextWarning     = 'WarningMsg'       ,