Fix epic board blocked icon when using epic color

What does this MR do and why?

Fixes displaying blocked icon with popover on epic boards when :epic_color_highlight feature flag is on.

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Enable :epic_color_highlight feature flag
2. Ensure one of the epic is blocked (add is blocked by relationship on the epic page)
3. Visit epic boards
4. The blocked icon should display on the corresponding epic card and show a popover on hover.

MR acceptance checklist

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