patch 8.1.2287: using EndOfBuffer highlight in popup does not look good

Problem:    Using EndOfBuffer highlight in popup does not look good.
Solution:   Do not EndOfBuffer highlight. (closes #5204)
diff --git a/src/testdir/test_popupwin.vim b/src/testdir/test_popupwin.vim
index 52d5add..ed4a775 100644
--- a/src/testdir/test_popupwin.vim
+++ b/src/testdir/test_popupwin.vim
@@ -12,6 +12,7 @@
 	call setline(1, range(1, 100))
 	hi PopupColor1 ctermbg=lightblue
 	hi PopupColor2 ctermbg=lightcyan
+	hi EndOfBuffer ctermbg=lightgrey
 	hi Comment ctermfg=red
 	call prop_type_add('comment', #{highlight: 'Comment'})
 	let winid = popup_create('hello there', #{line: 3, col: 11, minwidth: 20, highlight: 'PopupColor1'})