ci: derive prerelease NuGet version dynamically from project version

Author: Copilot

.github/workflows/prerelease.yml

@@ -19,8 +19,9 @@ jobs:
 
       - name: Determine prerelease version
         run: |
+          BASE_VERSION=$(grep -oPm1 "(?<=<Version>)[^<]+" src/Directory.Build.props)
           COMMIT_SHA=$(git rev-parse --short HEAD)
-          echo "PRERELEASE_VERSION=11.0.0-${COMMIT_SHA}" >> $GITHUB_ENV
+          echo "PRERELEASE_VERSION=${BASE_VERSION}-${COMMIT_SHA}" >> $GITHUB_ENV
 
       - name: Setup .NET
         uses: actions/setup-dotnet@v1