Fix typos in pcbnew sub-directory

Found via `codespell -q 3 -S *.po,./thirdparty,./Documentation/changelogs -L aactual,acount,aline,alocation,alog,anormal,anumber,aother,apoints,aparent,aray,ba,busses,dout,einstance,leaded,modul,ontext,ot,overide,serie,te,,tesselate,tesselator,tht`

pcbnew/python/plugins/FootprintWizardBase.py

@@ -454,7 +454,7 @@ class FootprintWizardDrawingAids:
     def SetLineTickness(self, lineThickness):
         """!
         Old version of SetLineThickness.
-        Does the same thing, but is is only here for compatibility with old
+        Does the same thing, but is only here for compatibility with old
         scripts.
         Set the current pen lineThickness used for subsequent drawing
         operations