[BUG] You cannot swap weapons/gear while casting

[Rowain3]

1. Current Behavior

1.1. Description

You cannot swap weapons/gear while using a spell (also applies to mounts since they're technically spells) with a cast time

1.2. How to Reproduce

       1. Make a mage
       2. Use frostbolt or any spell with a cast time longer than the GCD
       3. Try to swap weapons/gear (gear while out of combat) during cast

1.3 Source Material

https://gyazo.com/c843d19288bfd2db541bd7b78adca824

2. Expected Behavior

2.1. Description

You should be able to swap weapons/gear while casting something

2.2 Source Material

https://www.youtube.com/watch?v=GYUbaSCjCTU&t=320s
https://i.imgur.com/sW9zNah.png

[raethkcj]

Archive of the official patch note for additional reference: https://web.archive.org/web/20130129032406/http://us.battle.net/wow/en/game/patch-notes/2-4-3