Fixed #19096 - More extendable can_return_id_from_insert

RETURNING is an extension of the SQL standard, which is not implemented
the same by all databases. Allow DatabaseOperations.return_insert_id to
return a None to allow for other 3rd party backends with a different
implementation.

django/db/models/sql/compiler.py

@@ -897,8 +897,9 @@ def as_sql(self):
             col = "%s.%s" % (qn(opts.db_table), qn(opts.pk.column))
             result.append("VALUES (%s)" % ", ".join(placeholders[0]))
             r_fmt, r_params = self.connection.ops.return_insert_id()
-            result.append(r_fmt % col)
-            params += r_params
+            if r_fmt:
+                result.append(r_fmt % col)
+                params += r_params
             return [(" ".join(result), tuple(params))]
         if can_bulk:
             result.append(self.connection.ops.bulk_insert_sql(fields, len(values)))