Temporary enable transient-mark-mode for rectangle selection

* lisp/mouse.el (mouse-drag-region-rectangle):
Enable transient-mark-mode during selection (bug#38431).
1 job for master in 97 minutes and 52 seconds (queued for 2 seconds)
Status Job ID Name Coverage
failed #4404


Name Stage Failure
test-all Test The script exceeded the maximum execution time set for the job

In end of data:
lisp/mail/footnote-tests.el:48:1:Warning: the following functions are not
known to be defined: footnote-add-footnote, footnote-back-to-message
GEN lisp/mail/footnote-tests.log
ELC lisp/mail/rfc2047-tests.elc
GEN lisp/mail/rfc2047-tests.log
Pulling docker image gitlab/gitlab-runner-helper:x86_64-d0b76032 ...
ERROR: Job failed: execution took longer than 1h30m0s seconds