Adjust fuzzing to run on main branch only

Author: stephane

.github/workflows/cifuzz.yml

@@ -0,0 +1,29 @@
+name: Fuzzing
+on:
+    push:
+        branches: ["master"]
+
+jobs:
+    fuzzing:
+        runs-on: ubuntu-latest
+        steps:
+            - name: Build Fuzzers
+              id: build
+              uses: google/oss-fuzz/infra/cifuzz/actions/build_fuzzers@master
+              with:
+                  oss-fuzz-project-name: "libmodbus"
+                  dry-run: false
+                  language: c
+            - name: Run Fuzzers
+              uses: google/oss-fuzz/infra/cifuzz/actions/run_fuzzers@master
+              with:
+                  oss-fuzz-project-name: "libmodbus"
+                  fuzz-seconds: 300
+                  dry-run: false
+                  language: c
+            - name: Upload artifacts
+              uses: actions/upload-artifact@v3
+              if: failure() && steps.build.outcome == 'success'
+              with:
+                  name: artifacts
+                  path: ./out/artifacts