CI caching

.github/workflows/main.yml

@@ -6,10 +6,7 @@ on:
       - master
       - dev
   pull_request:
-    types: [opened, reopened]
-    branches:
-      - master
-      - dev
+    types: [opened, synchronize, reopened]
 jobs:
   test:
 
@@ -21,6 +18,10 @@ jobs:
 
     steps:
       - uses: actions/checkout@v2
+      - uses: actions/cache@v1
+        with:
+          path: ~/.cache/pip
+          key: ${{ runner.os }}-pip-${{ matrix.python-version }}-${{ hashFiles('**/setup.py') }}
       - name: Set up Python ${{ matrix.python-version }}
         uses: actions/setup-python@v2
         with: