Improve CI flow

.github/workflows/main.yml

@@ -9,6 +9,7 @@ on:
 jobs:
   tests:
     runs-on: ${{ matrix.os }}
+    if: github.event_name == 'pull_request'
     strategy:
       matrix:
         os: [ubuntu-latest, macos-latest, windows-latest]
@@ -36,7 +37,7 @@ jobs:
 
   build_publish:
     runs-on: ubuntu-latest
-    if: github.event_name == 'push'
+    if: github.event_name == 'push' && startsWith(github.ref, 'refs/tags')
     steps:
       - uses: actions/checkout@v2
 
@@ -48,7 +49,7 @@ jobs:
       - name: Install tools
         run: |
           python -m pip install --upgrade pip
-          pip install twine
+          pip install twine wheel
 
       - name: Build
         run: |