Change the ci.yml file to use the paid runner when running from FreeR…

…TOS, and use a free ubuntu-20.04 runner if run from a users fork

.github/workflows/ci.yml

@@ -198,8 +198,8 @@ jobs:
           config: .github/memory_statistics_config.json
           check_against: docs/doxygen/include/size_table.md
 
-  proof_ci:
-    if: ${{ github.event.pull_request }}
+  proof_ci_cbmc_runner:
+    if: ${{ github.event.repository.owner }} == "FreeRTOS"
     runs-on: cbmc_ubuntu-latest_16-core
     steps:
       - name: Set up CBMC runner
@@ -211,3 +211,17 @@ jobs:
         uses: FreeRTOS/CI-CD-Github-Actions/run_cbmc@main
         with:
           proofs_dir: test/cbmc/proofs
+
+  proof_ci_ubuntu_runner:
+    if: ${{ github.event.repository.owner }} != "FreeRTOS"
+    runs-on: ubuntu-20.04
+    steps:
+      - name: Set up CBMC runner
+        uses: FreeRTOS/CI-CD-Github-Actions/set_up_cbmc_runner@main
+        with:
+          cbmc_version: "5.61.0"
+          cbmc_viewer_version: "3.5"
+      - name: Run CBMC
+        uses: FreeRTOS/CI-CD-Github-Actions/run_cbmc@main
+        with:
+          proofs_dir: test/cbmc/proofs