Support vcpkg in Dependabot (#1353)

[Dependabot now supports
`vcpkg`](https://github.blog/changelog/2025-08-12-dependabot-version-updates-now-support-vcpkg/)

Author: JackPGreen

.github/dependabot.yml

@@ -1,5 +1,9 @@
 version: 2
 updates:
+  - package-ecosystem: "vcpkg"
+    directory: "/"
+    schedule:
+      interval: "weekly"
   - package-ecosystem: "github-actions"
     directory: "/"
     schedule: