Install .NET 6.0 when running tests

Fixes #1001.

Author: jskeet

.github/workflows/test-examples.yaml

@@ -23,10 +23,16 @@ jobs:
     - name: Check out our repo
       uses: actions/checkout@v2
 
-    - name: Setup .NET 8.0
-      uses: actions/setup-dotnet@v1
+    # We build examples against .NET 6.0, but use
+    # 8.0 for the tools themselves. (The closer we
+    # are to the target language version we're standardising,
+    # the better.)
+    - name: Setup .NET 6.0 and 8.0
+      uses: actions/setup-dotnet@v3
       with:
-        dotnet-version: 8.0.x
+        dotnet-version: |
+          6.0.x
+          8.0.x
 
     - name: Extract and validate tests
       run: |