ChatControlBase: Fix scroll hotkey infinite recursion

Handling of SHIFT + PAGE_UP/PAGE_DOWN was missing in the
ConversationTextview key press handler
3 jobs for master in 3 minutes and 27 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
passed #20173
run-appdata

00:00:06

failed #20172
run-tests

00:03:21

 
  Build
skipped #20174
run-build
 
Name Stage Failure
failed
run-tests Test
Ran 1 test in 0.000s

OK
$ codespell -I codespell.conf --skip="*__pycache__*,gajim/data/icons,gajim/data/sounds,gajim/data/emoticons" gajim
gajim/dialogs.py:354: trasform ==> transform
gajim/data/style/gajim.css:11: trough ==> through
Running after_script
Uploading artifacts for failed job
ERROR: Job failed: exit status 1