Update Textual to 0.26.0

Both issues I opened have been fixed! :)

README.md

@@ -195,8 +195,6 @@ To preview ANSI art files in file managers like Nautilus, Thunar, Nemo, or Caja,
 - Menu items like Copy/Cut/Paste are not grayed out when inapplicable. Only unimplemented items are grayed out.
 - Set As Wallpaper may not work on your system. For me, on Ubuntu, the wallpaper setting is updated but the picture is not, unless I manually pick it. There is however untested support for many platforms, and you may have better luck than me.
 - If you paste and then stamp the selection with Ctrl+Click, the stamp(s) can't be undone. An undo state is only created when finalizing the selection, for pasted selections.
-- Pasting with middle click can crash the program if the clipboard is empty. See [textual issue #2563](https://github.com/Textualize/textual/issues/2563)
-- Clicking a folder in the file dialogs can cause the program to exit if there's a permission error. See [textual issue #2564](https://github.com/Textualize/textual/issues/2564)
 - The Open dialog's file tree view doesn't scroll down to the initially selected file/folder.
 - ANSI files (.ans) are treated as UTF-8 when saving and loading, rather than CP437 or Windows-1252 or any other encodings. Unicode is nice and modern terminals support it, but it's not the standard for ANSI files. There isn't really a standard for ANSI files.
 - ANSI files are loaded with a white background. This may make sense as a default for text files, but ANSI files either draw a background or assume a black background, being designed for terminals.

requirements.txt

@@ -7,5 +7,5 @@ pyperclip==1.8.2
 pyxdg==0.28
 rich==13.3.5
 stransi==0.3.0
-textual[dev]==0.24.1
+textual[dev]==0.26.0
 watchdog==3.0.0