Add dotnet tools manifest directory to dependabot nuget ecosystem

Agent-Logs-Url: https://github.com/IntelliTect/EssentialCSharp.Web/sessions/b3cc0f98-2cc6-4465-99d1-66356dc3556f

Co-authored-by: BenjaminMichaelis <22186029+BenjaminMichaelis@users.noreply.github.com>

Author: Copilot

.github/dependabot.yml

@@ -13,6 +13,7 @@ updates:
   - package-ecosystem: "nuget" # See documentation for possible values
     directories:
       - "/"
+      - "/.config"
     registries:
       - nuget-azure-artifacts
     schedule: