Fix memory leak of rebinned histograms in ShapeTools

Mark the TList that holds the rebinned histograms as the owner of the
contained objects, so that they get properly deleted after PyROOT
reliquishes the ownership during `TList::Add()`.

This was detected by the strict memory policy in ROOT master
(root-project/root#13593), where this ownership
problem manifested as a segfault from dangling references.

Author: guitargeek

python/ShapeTools.py

@@ -946,6 +946,7 @@ def getPdf(self, channel, process, _cache=None):
         if self.options.useHistPdf != "always":
             if nominalPdf.InheritsFrom("TH1"):
                 rebins = ROOT.TList()
+                rebins.SetOwner(True)  # The list takes ownership of the rebinned histograms
                 maxbins = 0
                 for i in range(pdfs.GetSize()):
                     rebinned = self.rebinH1(pdfs.At(i))