configure.ac: bump versions for the 2.10.16 release

3 jobs for GIMP_2_10_16 in 21 minutes and 7 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Babl
passed #598722
babl-git

00:05:35

 
  Gegl
passed #598723
gegl-git

00:03:17

 
  Gimp
passed #598724
build-git-autotools

00:12:13