Correct issue with VCS staged color

Correct OHMYVIAREZO_VCS_COLOR_STAGED variable name so that it can be sued without glitch in the rest of the theme

This variable contains the color used to display VCS when changes are staged but not yet committed, it is used in line 66.

Before this correction, this mistake in the variable name created a small glitch (A "S" character that isn't supposed to be there + the color used for VCS is the one used from the previous status before staged instead of the staged color)

After the correction, this glitch does not appear anymore, and the VCS is displayed with the staged color