Diff PRs should target dotnet repo

[mthalman]

PRs that get generated for diffs of SDK files and license scan output should now be targeting the dotnet repo instead of sdk. This is because those PRs are attempting to modify files located in the src/SourceBuild/content path but everything in that path has been removed from the sdk repo: dotnet/sdk#48695. Those files should now be modified directly from the dotnet repo.