chore: vouch gtremper (#4648)

<!-- ccr-slack-attribution -->
_Requested by **Matt Aitken** · [Slack
thread](https://triggerdotdev.slack.com/archives/C045W9WM3E1/p1786948064703889?thread_ts=1786948064.703889&cid=C045W9WM3E1)_

Adds `gtremper` to `.github/VOUCHED.td`.

Before: PRs from `gtremper` are auto-closed by the vouch check.
After: `gtremper` is vouched, so their PRs stay open and run CI.

Done as a direct file edit rather than the issue-comment flow because
there is no open Vouch Request issue for this user, matching the
precedent in #3804.

Co-authored-by: Claude <noreply@anthropic.com>

Author: claude[bot]

.github/VOUCHED.td

@@ -28,4 +28,5 @@ brentshulman-silkline
 Leafgard
 Rohan170603
 NERLOE
-Jakub-Vacek
+Jakub-Vacek
+gtremper