Minor issue in 3.21 release notes

[gegles]

@swlars , very minor thing but the 3.21 release notes link to the wrong PR for the GSO/GRO feature... It is #1926 when it should be #1925

Thanks in advance!

[swlars]

Thanks! I updated it on github, but it might take a bit to fix in the RELNOTES file.

[gegles]

That's Ok @swlars, the github was the more important one I think, thanks!