Update build.yml

Get fork PR tests running

.github/workflows/build.yml

@@ -7,6 +7,11 @@ on:
   pull_request:
     branches:
       - master
+  workflow_run:
+    workflows:
+      - 'pytorch-widedeep'
+    types:
+      - requested
 
 jobs:
   codestyle:
@@ -83,4 +88,4 @@ jobs:
     - name: upload coverage to Codecov
       uses: codecov/codecov-action@v1
       with:
-        fail_ci_if_error: true
\ No newline at end of file
+        fail_ci_if_error: true