Bump CBMC version to very latest release

Author: tautschnig

.github/workflows/ci.yml

@@ -406,7 +406,7 @@ jobs:
       - name: Set up CBMC runner
         uses: FreeRTOS/CI-CD-Github-Actions/set_up_cbmc_runner@main
         with:
-          cbmc_version: "6.1.1"
+          cbmc_version: "6.3.1"
 
       - env:
           stepName: Install Dependencies