bpo-34120: fix text viewer to call grab_release() only when needed (GH-8616)

(cherry picked from commit dd74369cb7)

Co-authored-by: Tal Einat <taleinat+github@gmail.com>

Lib/idlelib/textview.py

@@ -83,7 +83,8 @@ class ViewWindow(Toplevel):
                                             command=self.ok, takefocus=False)
         self.viewframe.pack(side='top', expand=True, fill='both')
 
-        if modal:
+        self.is_modal = modal
+        if self.is_modal:
             self.transient(parent)
             self.grab_set()
             if not _utest:
@@ -91,7 +92,8 @@ class ViewWindow(Toplevel):
 
     def ok(self, event=None):
         """Dismiss text viewer dialog."""
-        self.grab_release()
+        if self.is_modal:
+            self.grab_release()
         self.destroy()