I claim the ornamental design for an egg holder, as shown and described.
FIG. 1 is a bottom perspective view of an egg holder showing my new design, the broken lines are for illustrative purposes only and form no part of the claimed design.
FIG. 2 is a top perspective view thereof.
FIG. 3 is a right side view thereof.
FIG. 4 is a left side view thereof.
FIG. 5 is a front view thereof.
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The broken line portions representing the front end and rear end thereof form no part of the claimed invention.