[TreeProcMT][NFC] Use modern TFile::Get overload
[TreeProcMT][NFC] Use modern TFile::Get overload

root-mirror/root,karies/root,olifre/root,root-mirror/root,karies/root,karies/root,karies/root,karies/root,root-mirror/root,olifre/root,olifre/root,root-mirror/root,olifre/root,root-mirror/root,root-mirror/root,olifre/root,karies/root,olifre/root,olifre/root,root-mirror/root,root-mirror/root,karies/root,karies/root,karies/root,root-mirror/root,olifre/root,karies/root,karies/root,olifre/root,olifre/root,root-mirror/root,root-mirror/root,olifre/root