* lisp/gnus: Use `with-current-buffer` at a few more places

* lisp/gnus: Use `with-current-buffer` at a few more places

* lisp/gnus/nnmbox.el (nnmbox-request-scan, nnmbox-read-mbox):
* lisp/gnus/nnmairix.el (nnmairix-create-search-group):
* lisp/gnus/nnfolder.el (nnfolder-existing-articles):
* lisp/gnus/nndraft.el (nndraft-auto-save-file-name):
* lisp/gnus/nndoc.el (nndoc-request-article):
* lisp/gnus/nnbabyl.el (nnbabyl-read-mbox):
* lisp/gnus/gnus-score.el (gnus-score-body):
* lisp/gnus/gnus-start.el (gnus-dribble-enter)
(gnus-dribble-eval-file, gnus-ask-server-for-new-groups)
(gnus-read-newsrc-file, gnus-read-descriptions-file):
* lisp/gnus/gnus-spec.el (gnus-update-format-specifications):
* lisp/gnus/gnus-draft.el (gnus-draft-edit-message):
* lisp/gnus/gnus-art.el (gnus-request-article-this-buffer)
(gnus-article-edit-exit): Use `with-current-buffer`.