ConversationListView: Fix shift-to-delete inversion

The 'Is Shift down' condition was accidentally inverted in commit
419bc6d0, resulting in inconsistency
between the main toolbar and a conversations list context menu.
4 jobs for fix-move-to-trash in 6 minutes and 42 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  .Pre
failed #592123
flatpak

00:06:42

failed #592118
flatpak

00:05:07

 
  Build
skipped #592119
fedora
skipped #592120
ubuntu
 
Name Stage Failure
failed
flatpak .Pre
make: *** [Makefile:446: all] Error 2
Error: module gmime: Child process exited with code 2
Uploading artifacts...
WARNING: geary-dev.flatpak: no matching files
WARNING: repo/: no matching files
WARNING: _build/meson-logs/meson-log.txt: no matching files
WARNING: _build/meson-logs/testlog.txt: no matching files
ERROR: No files to upload
ERROR: Job failed: exit code 1