fix: update workflow

.github/workflows/validate.yml

@@ -1,20 +1,22 @@
 name: validate
 on:
-- push
-- pull_request
+  push:
+    branches:
+    - 'master'
+  pull_request:
+    branches:
+    - '**'
 jobs:
   tests:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        node-version:
-        - 12
         node: [12, 14, 16]
     steps:
     - uses: actions/checkout@v2
     - uses: actions/setup-node@v2
       with:
-        node-version: ${{ matrix.node-version }}
+        node-version: ${{ matrix.node }}
     - run: make validate.ci
     - name: Upload coverage
       uses: codecov/codecov-action@v2