Backport PR #9953: corrected split with rsplit

sir, _Carreau i changed the split with rsplit, i did it because with split only the first that is splitted from the string is taken, but with rsplit the last string is taken, which is what we want. please verify sir.

IPython/core/magics/execution.py

@@ -437,7 +437,7 b' python-profiler package from non-free.""")'
 
     def _debug_exec(self, code, breakpoint):
         if breakpoint:
-            (filename, bp_line) = breakpoint.split(':', 1)
+            (filename, bp_line) = breakpoint.rsplit(':', 1)
             bp_line = int(bp_line)
         else:
             (filename, bp_line) = (None, None)