Ensure line numbers are updated (DistributedProofreaders#229)

Where a key press was handled too early (perhaps keystrokes that
are bound to the class rather than the instance) it did not then
also trigger the KeyPress event binding that updates the line
numbers. Using KeyRelease instead works fine, and is the simplest
and safest fix IMO.

src/guiguts/maintext.py

@@ -112,7 +112,8 @@ def __init__(self, parent: tk.Widget, root: tk.Tk, **kwargs: Any) -> None:
         self.linenumbers = TextLineNumbers(self.frame, self)
         self.linenumbers.grid(column=0, row=0, sticky="NSEW")
         self.bind_event("<Configure>", self._on_change, add=True, force_break=False)
-        self.bind_event("<KeyPress>", self._on_change, add=True, force_break=False)
+        # Use KeyRelease not KeyPress since KeyPress might be caught earlier and not propagated to this point.
+        self.bind_event("<KeyRelease>", self._on_change, add=True, force_break=False)
         self.numbers_need_updating = True
 
         def hscroll_set(*args: Any) -> None: