enable workflow dispatch for CI CPP (#2964)

* enable workflow dispatch

* enable workflow dispatch

Author: agunapal

.github/workflows/ci-cpu-cpp.yml

@@ -1,12 +1,10 @@
 name: CI CPU - CPP Build
 
 on:
+  workflow_dispatch:
   push:
     branches:
       - master
-  pull_request:
-    branches:
-      - master
 
 concurrency:
   group: ci-cpu-${{ github.workflow }}-${{ github.ref == 'refs/heads/master' && github.run_number || github.ref }}