Open new entry in changelog

As explained at[1], piuparts job setup local repository with packages
just built. If their version is equal to version in archives, job will
fail with "Sources disagree on hashes of supposely identical version"
error. So, to keep CI clean, it is necessary to create new changelog
entry after release.

 [1] salsa-ci-team/pipeline#46 (comment 80587)
8 jobs for master in 27 minutes and 7 seconds (queued for 4 seconds)
latest
Status Job ID Name Coverage
  Build
passed #279762
build

00:03:49

 
  Test
passed #279767
autopkgtest

00:03:14

passed #279768
blhc

00:01:31

passed #279766
lintian

00:01:51

passed #279769
piuparts

00:05:18

passed #279765
reprotest

00:04:08

passed #279764
test-build-all

00:03:30

passed #279763
test-build-any

00:03:42