Update actions/checkout action to v3 (#3118)

Author: renovate[bot]

.github/workflows/NetCoreTests.yml

@@ -52,7 +52,7 @@ jobs:
       run: |
         docker run -d -p 1521:1521 -e APP_USER=nhibernate -e APP_USER_PASSWORD=nhibernate -e ORACLE_PASSWORD=nhibernate gvenzl/oracle-xe:18-slim
 
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
     - name: Setup .NET
       uses: actions/setup-dotnet@v2
       with: