Group names are wrongly formatted for tab styled group separators

[JoannesJ]

display_name isn't used for tab styled group separators.
This leads to e.g. "test name" being displayed as "test_name".

bufferline.nvim/lua/bufferline/groups.lua

Lines 68 to 77 in d6cb9b7

	function separator.tab(group, hls, count)
	local hl = hls.fill.hl_group
	local indicator_hl = hls.buffer.hl_group
	local indicator = {
	{ highlight = hl, text = C.padding },
	{ highlight = indicator_hl, text = C.padding .. group.name .. count .. C.padding },
	{ highlight = hl, text = C.padding },
	}
	return { sep_start = indicator, sep_end = space_end(hls) }
	end

[akinsho]

@JoannesJ if you could raise a PR for this fix that would be much appreciated 🚀