fix: Use GitVersion 5.x

6.x was generating incorrect version numbers for the hotfixes.

(cherry picked from commit 980def2)

.github/workflows/dotnet.yml

@@ -33,7 +33,7 @@ jobs:
     - name: Install GitVersion
       uses: gittools/actions/gitversion/setup@v1
       with:
-        versionSpec: '6.x'
+        versionSpec: '5.x'
         includePrerelease: true
         preferLatestVersion: true