The treatment of ${\text{CH}}_3\text{MgX}$ with ${\text{CH}}_3\text{C}\equiv \text{C}-\text{H}$ produces:

Grignard reagents ($\text{RMgX}$) react with compounds containing active hydrogen (like terminal alkynes, alcohols, acids, water) to produce alkanes.
$${\text{CH}}_3\text{MgX}+\text{H}-\text{C}\equiv \text{C}-{\text{CH}}_3\to {\text{CH}}_4+\text{XMg}-\text{C}\equiv \text{C}-{\text{CH}}_3$$
The methyl group of the Grignard reagent combines with the acidic hydrogen of the alkyne to form methane (${\text{CH}}_4$).