update the build workflow to work on the restructured repo

Author: tmthecoder

.github/workflows/dart-build.yml

@@ -2,9 +2,7 @@ name: dargon2
 
 on:
   push:
-    branches: [ main ]
   pull_request:
-    branches: [ main ]
 
 jobs:
   test:
@@ -13,6 +11,8 @@ jobs:
       image:  google/dart:latest
     steps:
     - uses: actions/checkout@v2
+    - name: move to dargon2 main lib
+      run: cd dargon2
     - name: Install dependencies
       run: pub get
     - name: Run tests