Protected tags release notes field should follow the tag's permission settings
Proposal
The docs say "Protected tags prevent anyone from updating or deleting the tag, and prevent creation of matching tags based on the permissions you have selected. By default, anyone without Maintainer permissions is prevented from creating tags." (source, emphasis mine)
However, protected tags can have their release notes field updated by users with lower permissions than Maintainer when Maintainer is selected as the permission level.
The ability to edit the release notes field of a protected tag should follow the convention of the permissions selected for the tag (i.e. Maintainer only, Maintainer + Developer, No One, or specific users). Alternatively, there should be a separate setting specifically for the ability to edit the release notes field.