(build) Install .NET 7.0 on build machine

This is needed based on the current target frameowrks that are in place.
This SDK must have been removed on the GitHub Build machines, now that
.NET 9.0 is available.

Author: gep13

.github/workflows/build.yml

@@ -43,14 +43,15 @@ jobs:
       - name: Fetch all tags and branches
         run: git fetch --prune --unshallow
 
-      - name: Install .NET SDK 2.1.x, 3.1.x, 5.0.x, and 6.0.x
+      - name: Install .NET SDK 2.1.x, 3.1.x, 5.0.x, 6.0.x, and 7.0.x
         uses: actions/setup-dotnet@v4
         with:
           dotnet-version: |
             2.1.x
             3.1.x
             5.0.x
             6.0.x
+            7.0.x
 
       - name: Cache Tools
         uses: actions/cache@v4