Bump TheRock to 7.13.0a20260421 (#360)

## Summary
Automated nightly TheRock version bump.

| Dependency | Old | New |
|------------|-----|-----|
| TheRock | `7.13.0a20260420` | `7.13.0a20260421` |

Auto-generated by
[`bump-deps.yml`](https://github.com/iree-org/fusilli/blob/main/.github/workflows/bump-deps.yml).

Signed-off-by: iree-pr-automator[bot] <iree-github-actions-bot@google.com>
Co-authored-by: iree-pr-automator[bot] <iree-github-actions-bot@google.com>
Co-authored-by: Sambhav Jain <sambhav@alumni.stanford.edu>

Author: 3 people

version.json

@@ -1,5 +1,5 @@
 {
   "package-version": "0.0.1.dev",
   "iree-version": "3.12.0rc20260421",
-  "therock-version": "7.13.0a20260420"
+  "therock-version": "7.13.0a20260421"
 }