Update latest workflow ref

Author: Shaptic

.github/workflows/horizon.yml

@@ -14,7 +14,7 @@ jobs:
   horizon:
     # TODO: pin to a SHA on stellar-horizon main (like rpc.yml does) once the
     # callable-tests branch is merged.
-    uses: stellar/stellar-horizon/.github/workflows/integration-tests.yml@callable-tests
+    uses: stellar/stellar-horizon/.github/workflows/integration-tests.yml@aab88906f6eadcc30e61a57ec0b11667a9cff160
     with:
       horizon_git_ref: protocol-next
       core_git_ref: ${{ github.sha }}