Fix docs.yml

Author: vzarytovskii

.github/workflows/docs.yml

@@ -45,6 +45,8 @@ jobs:
       - name: Build FSharp.Formatting main
         run: dotnet fsi ./build.fsx -t Build
         working-directory: ${{ env.FSF_DIR }}
+      - name: Build local FSharp.Core project in current repo
+        run: dotnet build --restore FSharp.Core/FSharp.Core.fsproj
       - name: Run fsdocs
         run: dotnet FSharp.Formatting/src/fsdocs-tool/bin/Release/net6.0/fsdocs.dll build --sourcefolder ${{ env.FSHARP_DIR }}
       - name: Deploy