D26942: Fix kwin.upd not running if python 2 not installed

fvogt created this revision.
fvogt added a reviewer: Plasma.
Herald added a project: KWin.
Herald added a subscriber: kwin.
fvogt requested review of this revision.

REVISION SUMMARY
  If the listed interpreter does not exist, kconf_update skips the update.
  The update script uses python3, so declare that properly.

TEST PLAN
  Saw the error by accident, it's gone now.

REPOSITORY
  R108 KWin

BRANCH
  Plasma/5.18

REVISION DETAIL
  https://phabricator.kde.org/D26942

AFFECTED FILES
  kconf_update/kwin.upd

To: fvogt, #plasma
Cc: kwin, plasma-devel, Orage, LeGast00n, The-Feren-OS-Dev, jraleigh, zachus, fbampaloukas, GB_2, mkulinski, ragreen, jackyalcine, iodelay, crozbo, bwowk, ZrenBot, ngraham, alexeymin, himcesjf, lesliezhai, ali-mohamed, hardening, romangg, jensreuterberg, abetts, sebas, apol, ahiemstra, mart