Fix reports printing twice when called from Python in background-mode

Calling operators in background-mode always printed with the
assumption that output should never be hidden.
However operators called from `bpy.ops` were also printing reports to
the `stdout` (needed for the Python console and generally useful).

Resolve by adding a flag to signal that the owner of the ReportList
is responsible for printing to the `stdout`.

source/blender/python/intern/bpy_operator.c

@@ -289,7 +289,7 @@ static PyObject *pyop_call(PyObject *UNUSED(self), PyObject *args)
       reports = MEM_mallocN(sizeof(ReportList), "wmOperatorReportList");
 
       /* Own so these don't move into global reports. */
-      BKE_reports_init(reports, RPT_STORE | RPT_OP_HOLD);
+      BKE_reports_init(reports, RPT_STORE | RPT_OP_HOLD | RPT_PRINT_HANDLED_BY_OWNER);
 
 #ifdef BPY_RELEASE_GIL
       /* release GIL, since a thread could be started from an operator