fix(test): suppress Vim message truncation in testutil with.ts

Add `shortmess-=T` to Vim startup options alongside `columns=9999` to
prevent Vim from truncating long messages during test runs.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: lambdalisue

tests/denops/testutil/with.ts

@@ -56,7 +56,7 @@ export function withVim<T>(
     "-c",
     "visual", // Go to Normal mode
     "-c",
-    "set columns=9999", // Avoid unwilling output newline
+    "set columns=9999 shortmess-=T", // Avoid unwilling output newline/truncation
     ...commands.flatMap((c) => ["-c", c]),
   ];
   return withProcess(cmd, args, { verbose: conf.verbose, ...options });