Fix incorrect tick delta capture for 1.21

[celestialfault]

Fixes #36

[what-the-diff[bot]]

PR Summary

• Introduction of Delta Variable to GuiMixin.java The update introduces a new piece of code to the GuiMixin.java file - a floating point variable called 'delta'. This variable captures and holds the 'partial tick' value from the game time delta. In non-technical terms, this means the 'delta' variable keeps track of small time intervals (or 'ticks') within the game, which can provide more precision and control over certain game actions.

[tr7zw]

Good catch