Small fix to writing Gnus dribble change-level entries

* lisp/gnus/gnus-start.el (gnus-group-change-level): PREVIOUS needs to
  still be a string when the dribble entry is written, so don't
  convert it to an entry until after that's done. Also, we're not
  meant to write PREVIOUS itself, we're meant to write the group that
  comes _after_ it in the sort-order of gnus-group-list, so do that
1 job for master in 51 minutes and 32 seconds (queued for 4 seconds)
Status Job ID Name Coverage
failed #2362


Name Stage Failure
test-all Test
make[2]: *** [check-doit] Error 1
Makefile:318: recipe for target 'check-doit' failed
make[2]: Leaving directory '/builds/emacs/emacs/test'
Makefile:293: recipe for target 'check-expensive' failed
make[1]: *** [check-expensive] Error 2
make[1]: Leaving directory '/builds/emacs/emacs/test'
make: *** [check-expensive] Error 2
Makefile:959: recipe for target 'check-expensive' failed
ERROR: Job failed: exit code 1