What version of protobuf and what language are you using?
Version: v3.21.5
Language: C#
OS: Windows 10

What did you do?
I have a protobuf schema, which has an enum, some of the enum values are no longer required and I want to deprecate them, I added deprecate = true with the values but it doesn't add the [Obsolete] attribute in the generated c# model
here is the code example

enum Months{
JANUARY = 0 [deprecated = true];
FEBRUARY = 1 [deprecated = true];
MARCH = 2 [deprecated = true];
APRIL = 3 [deprecated = true];
MAY = 4;
JUNE = 5 [deprecated = true];
JULY = 6 [deprecated = true];
AUGUST = 7;
SEPTEMBER = 8 [deprecated = true];
OCTOBER = 9;
NOVEMBER = 10;
DECEMBER = 11;
}