Don't use actions/checkout@master

See https://github.com/actions/toolkit/blob/master/docs/action-versioning.md

ci/azure.yml

@@ -23,7 +23,7 @@ jobs:
     name: Build and Deploy
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@master
+    - uses: actions/checkout@v1
     - name: Use Node.js ${{ env.NODE_VERSION }}
       uses: actions/setup-node@v1
       with:

ci/gem-push.yml

@@ -14,7 +14,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@master
+    - uses: actions/checkout@v1
     - name: Set up Ruby 2.6
       uses: actions/setup-ruby@v1
       with:

ci/google.yml

@@ -31,7 +31,7 @@ jobs:
     steps:
 
     - name: Checkout
-      uses: actions/checkout@master
+      uses: actions/checkout@v1
 
     # Setup gcloud CLI
     - uses: GoogleCloudPlatform/github-actions/setup-gcloud@master