Move *-pr private repo skips into sparse checkout template

For example [here](https://github.com/Azure/azure-sdk-for-net/blob/main/eng/pipelines/templates/jobs/ci.yml#L128). There are a few places across the NET and Java repos that skip sparse checkout for `-pr` suffixed repositories, because the current sparse checkout code does not work with the devops github auth token for private repositories.

We should consolidate these skips out of the repo yaml files and into the [sparse checkout template](https://github.com/Azure/azure-sdk-tools/blob/main/eng/common/pipelines/templates/steps/sparse-checkout.yml), so the behavior will default to a normal full clone when the repo is private. This likely has to be done with the devops template expression against the repo name, because the yaml needs to compile down to using the normal devops repo checkout yaml syntax otherwise, in order for the credentials to be used properly.