Set notifications repo name

Currently, pipeline runs of this repo create publish notification issues in the dotnet-docker-internal repo. These issues provide diagnostic info on success/failures that occur during publish. Given that this repo is managed separately from the official .NET Docker images, it makes sense for this repo to post its notifications to a separate repo. Instead, it can target [dotnet/dotnet-buildtools-prereqs-docker-internal](https://github.com/dotnet/dotnet-buildtools-prereqs-docker-internal). All that should be needed to do this is to override the `gitHubNotificationsRepoInfo.repo` variable. This gets defaulted [here](https://github.com/dotnet/dotnet-buildtools-prereqs-docker/blob/bb84b157841c4df1d27afbac42a3ddc896649106/eng/common/templates/variables/dotnet/build-test-publish.yml#L28-L29). The pipeline should override that value.