Update ci.yml

Allow manual triggering of build.

.github/workflows/ci.yml

@@ -1,10 +1,11 @@
 name: CI
 
-on:
+on: 
   push:
     branches: [ master ]
   pull_request:
     branches: [ master ]
+  workflow_dispatch:  
 
 jobs:
   build:
@@ -16,4 +17,4 @@ jobs:
       run: sudo apt-get install -y iverilog
     - uses: actions/checkout@v1
     - name: Run Tests
-      run: make test
+      run: make test