(#221) Update buil.yml to load .NET 7.0

Author: colinangusmackay

.github/workflows/build.yml

@@ -79,6 +79,11 @@ jobs:
         with:
           dotnet-version: 6.0.x # Always the latest patch version.
 
+      - uses: actions/setup-dotnet@v1
+        name: Setup .NET 7.0
+        with:
+          dotnet-version: 7.0.x # Always the latest patch version.
+
       - name: Build Solution
         run: dotnet build $STRAVAIG_SOLUTION --configuration Release