Specify the correct GHA reference and use P26

Author: Shaptic

.github/workflows/rpc.yml

@@ -12,8 +12,8 @@ concurrency:
 
 jobs:
   rpc:
-    name: RPC integration tests
-    uses: stellar/stellar-rpc/.github/workflows/integration-tests.yml@main
+    uses: stellar/stellar-rpc/.github/workflows/integration-tests.yml
     with:
+      rpc_git_ref: protocol-next
       core_git_ref: ${{ github.sha }}
-      protocol_version: '25'
+      protocol_version: '26'