From irc:

[11:25:10] <@mboddu> I dont mind tagged a f30 build into f31 (since all the gcc builds in f31 tag are from f30) but I wanted to make sure if I tag a new build, is it going to break anything
[11:27:03] <@jakub> mboddu: we have almost 500000 tests and the build looks good; of course, it is always possible it will break something, but perhaps better to find about that in rawhide than in f30
[11:28:06] <@mboddu> jakub: Okay, its just that as I dont know what things might have changed in the new build, I was concerned
[11:29:02] <@mboddu> tpopela: Can you open a releng ticket at pagure.io/releng so that it will tracked, rather than on irc
[11:29:11] mboddu: I can
[11:29:14] <@jakub> mboddu: gcc is now in a regression bugfixes and documentation fixes only mode and will remain in that mode until branched (and on the branch forever)
[11:29:16] <@mboddu> And if gcc maintainers are okay with it, I can tag the build
[11:29:26] <@jakub> mboddu: thanks

$ koji tag-build f31-pending gcc-9.0.1-0.10.fc30

Once signed, it should be available in f31 tag.