Bump github actions versions (#2171)

Part of #2169

.github/workflows/build.yml

@@ -18,7 +18,7 @@ jobs:
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v1
+        uses: actions/checkout@v2.4.0
 
       - name: Start PostgreSQL ${{ matrix.pg_major }} (Linux)
         if: startsWith(matrix.os, 'ubuntu')
@@ -72,7 +72,7 @@ jobs:
         shell: bash
 
       - name: Setup .NET Core SDK
-        uses: actions/setup-dotnet@v1
+        uses: actions/setup-dotnet@v1.9.0
 
       - name: Test
         run: dotnet test --configuration Debug --logger "GitHubActions;report-warnings=false"
@@ -85,10 +85,10 @@ jobs:
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v1
+        uses: actions/checkout@v2.4.0
 
       - name: Setup .NET Core SDK
-        uses: actions/setup-dotnet@v1
+        uses: actions/setup-dotnet@v1.9.0
 
       - name: Pack NuGet packages (CI versions)
         if: startsWith(github.ref, 'refs/heads/')