[Enhancement] add TIT3 frame in the list of ID3v2.4 variables

[SP-937-215]

Hello,

Could you please add "subtitle" (frame TIT3) in the list of available ID3v2.4 variables?

Thank you!

[Marekkon5]

Hello, TIT3 is in the list of abstractions, so it should be available in the tag fields. If it isn't, please try latest actions build, or you can directly just write TIT3 anyway.

[SP-937-215]

Thanks!