fix: Restore 'ses' to Dependabot config

Restores `ses` as an allowed dependency to update in the Dependabot config after it was accidentally removed in #729.

Author: rekmarks

.github/dependabot.yml

@@ -16,6 +16,7 @@ updates:
       - dependency-name: '@metamask/*'
       - dependency-name: '@agoric/*'
       - dependency-name: '@endo/*'
+      - dependency-name: 'ses'
 
   - package-ecosystem: 'github-actions'
     directory: '/'