Changed version schemed in installation from 2.1XX to 23.XX (#199)

* Changed version schemed in installation from 2.1XX to 23.XX

Another idea could be 2X.XX for future-proof, 24,25...

But thought it would be more confusing, and we can just change the value next year

* Update installing.md

Not a fan of XXX, 2XXX indicates to start the change filename after 2 (2.1XX for past versions and 2X.XX for newer) 

replacing the filename as appropriate -> replacing X with the filename as appropriate.

src/platform/linux/installing.md

@@ -31,8 +31,8 @@ To install Anki:
 3. Open a terminal and run the following commands, replacing the filename as appropriate.
 
 ```shell
-tar xaf Downloads/anki-2.1.XX-linux-qt6.tar.zst
-cd anki-2.1.XX-linux-qt6
+tar xaf Downloads/anki-2XXX-linux-qt6.tar.zst
+cd anki-2XXX-linux-qt6
 sudo ./install.sh
 ```