relnotes: copy "next" to "5.2" and clear "next"
This is the same thing as we did for 5.1 in
cba59b338976 (relnotes:
copy "next" to "5.1" and clear "next", 2019-08-01).
Differential Revision: https://phab.mercurial-scm.org/D7231
$ echo "[extensions]" >> $HGRCPATH
$ echo "mq=" >> $HGRCPATH
$ hg init
$ echo 'base' > base
$ hg ci -Ambase
adding base
$ hg qnew -mmqbase mqbase
$ hg qsave
$ hg qrestore 2
restoring status: hg patches saved state