Manual Reference: Includes the copyright

This was an oversight on the license headers copyright pass [1].

Also since the manual reference is generated by this script
we can update the copyright year every time.

[1] - 8f109712ee

tools/utils_doc/rna_manual_reference_updater.py

@@ -33,6 +33,7 @@ import os
 import argparse
 import re
 import sys
+import datetime
 
 try:
     import sphobjinv
@@ -73,8 +74,12 @@ def write_mappings(inv, output):
     # Write the file
     file = open(output, "w", encoding="utf-8")
     fw = file.write
+    year = datetime.date.today().year
 
+    fw(f"# SPDX-FileCopyrightText: 2019-%d Blender Foundation\n" % (year))
+    fw("#\n")
     fw("# SPDX-License-Identifier: GPL-2.0-or-later\n")
+    fw("\n")
     fw("# Do not edit this file.")
     fw(" This file is auto generated from rna_manual_reference_updater.py\n\n")
     # Prevent systems with autopep8 configured from re-formatting the file.