ci: pin GitHub Actions to SHA digests

Author: lhoupert

.github/workflows/ci.yml

@@ -10,9 +10,9 @@ jobs:
         python-version: [3.6, 3.7, 3.8, 3.9]
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@ee0669bd1cc54295c223e0bb666b733df41de1c5 # v2
       - name: Set up Python ${{ matrix.python-version }}
-        uses: actions/setup-python@v2
+        uses: actions/setup-python@e9aba2c848f5ebd159c070c61ea2c4e2b122355e # v2
         with:
           python-version: ${{ matrix.python-version }}
 
@@ -32,7 +32,7 @@ jobs:
 
       - name: Upload Results
         if: success()
-        uses: codecov/codecov-action@v1
+        uses: codecov/codecov-action@29386c70ef20e286228c72b668a06fd0e8399192 # v1
         with:
           file: ./coverage.xml
           flags: unittests
@@ -44,9 +44,9 @@ jobs:
     runs-on: ubuntu-latest
     if: contains(github.ref, 'tags')
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@ee0669bd1cc54295c223e0bb666b733df41de1c5 # v2
       - name: Set up Python
-        uses: actions/setup-python@v1
+        uses: actions/setup-python@0f07f7f756721ebd886c2462646a35f78a8bc4de # v1
         with:
           python-version: "3.x"