Convert formatting automatically to f-strings

Automatically convert formatting with the following call:
flynt -ll 2000 -v frappy*
Result: 303/381 auto-converted.
Failing conversions will be looked at manually in a follow-up commit.

Change-Id: Icd996b27221202faccc15af78e0380cf52ee37f2
Reviewed-on: https://forge.frm2.tum.de/review/c/secop/frappy/+/30900
Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de>
Reviewed-by: Georg Brandl <g.brandl@fz-juelich.de>
Reviewed-by: Alexander Zaft <a.zaft@fz-juelich.de>

frappy_psi/channelswitcher.py

@@ -145,7 +145,7 @@ class ChannelSwitcher(Drivable):
 
     def write_target(self, channel):
         if channel not in self._channels:
-            raise ValueError('%r is no valid channel' % channel)
+            raise ValueError(f'{channel!r} is no valid channel')
         if channel == self.target and self._channels[channel].enabled:
             return channel
         chan = self._channels[channel]