Fix test_popupwin failure due to syntax highlight change

This test is broken upstream, and needs to be fixed upstream in Vim.
Fixing it downstream for now to unblock CI.

Author: ychin

src/testdir/dumps/Test_popup_setbuf_04.dump

@@ -1,6 +1,6 @@
->*+0#ffffff16#ffd7ff255|h+0#e000002&|e|l|p|.|t|x|t|*+0#ffffff16&| +0#0000001&@5|F|o|r| |V+0#00e0e07&|i|m| |v|e|r|s|i|o|n| |9|.|1|.| +0#0000001&@1|L|a|s|t| |c|h|a|n|g|e|:| |2|0|2|4| |M|a|y| |2|7| @11| +0#0000000#0000001
+>*+0#ffffff16#ffd7ff255|h+0#e000002&|e|l|p|.|t|x|t|*+0#ffffff16&| +0#0000001&@5|F|o|r| |V+0#00e0e07&|i|m| |v|e|r|s|i|o|n| |9|.|1|.| +0#0000001&@1|L|a|s|t| |c|h|a|n|g|e|:| |2|0|2|5| |J|u|n| |2|7| @11| +0#0000000#0000001
 | +0#0000001#ffd7ff255@73| +0#0000000#a8a8a8255
-| +0#0000001#ffd7ff255@23|V|I|M| |-| |m|a|i|n| |h|e|l|p| |f|i|l|e| @29| +0#0000000#a8a8a8255
+| +0#0000001#ffd7ff255@23|V+0#00e0e07&|I|M| |-| |m|a|i|n| |h|e|l|p| |f|i|l|e| +0#0000001&@29| +0#0000000#a8a8a8255
 | +0#0000001#ffd7ff255@72|k| +0#0000000#a8a8a8255
 | +0#0000001#ffd7ff255@5|M|o|v|e| |a|r|o|u|n|d|:| @1|U|s|e| |t|h|e| |c|u|r|s|o|r| |k|e|y|s|,| |o|r| |"|h|"| |t|o| |g|o| |l|e|f|t|,| @11|h| @1| +0#0000000#a8a8a8255
 | +0#0000001#ffd7ff255|l| @71| +0#0000000#a8a8a8255

src/testdir/dumps/Test_popup_setbuf_05.dump

@@ -1,6 +1,6 @@
->h+0#e000002#ffffff0|e|l|p|.|t|x|t| +0#0000000&@7|F|o|r| |V+0#00e0e07&|i|m| |v|e|r|s|i|o|n| |9|.|1|.| +0#0000000&@1|L|a|s|t| |c|h|a|n|g|e|:| |2|0|2|4| |M|a|y| |2|7| @12
+>h+0#e000002#ffffff0|e|l|p|.|t|x|t| +0#0000000&@7|F|o|r| |V+0#00e0e07&|i|m| |v|e|r|s|i|o|n| |9|.|1|.| +0#0000000&@1|L|a|s|t| |c|h|a|n|g|e|:| |2|0|2|5| |J|u|n| |2|7| @12
 @75
-@24|V|I|M| |-| |m|a|i|n| |h|e|l|p| |f|i|l|e| @30
+@24|V+0#00e0e07&|I|M| |-| |m|a|i|n| |h|e|l|p| |f|i|l|e| +0#0000000&@30
 @73|k| 
 @6|M|o|v|e| |a|r|o|u|n|d|:| @1|U|s|e| |t|h|e| |c|u|r|s|o|r| |k|e| +0#0000001#ffd7ff255|s+0#0000000#ffffff0|,| |o|r| |"|h|"| |t|o| |g|o| |l|e|f|t|,| @11|h| @2
 |l| @73

src/testdir/dumps/Test_popup_setbuf_06.dump

@@ -1,6 +1,6 @@
->*+0#ffffff16#ffd7ff255|h+0#e000002&|e|l|p|.|t|x|t|*+0#ffffff16&| +0#0000001&@5|F|o|r| |V+0#00e0e07&|i|m| |v|e|r|s|i|o|n| |9|.|1|.| +0#0000001&@1|L|a|s|t| |c|h|a|n|g|e|:| |2|0|2|4| |M|a|y| |2|7| @11| +0#0000000#0000001
+>*+0#ffffff16#ffd7ff255|h+0#e000002&|e|l|p|.|t|x|t|*+0#ffffff16&| +0#0000001&@5|F|o|r| |V+0#00e0e07&|i|m| |v|e|r|s|i|o|n| |9|.|1|.| +0#0000001&@1|L|a|s|t| |c|h|a|n|g|e|:| |2|0|2|5| |J|u|n| |2|7| @11| +0#0000000#0000001
 | +0#0000001#ffd7ff255@73| +0#0000000#a8a8a8255
-| +0#0000001#ffd7ff255@23|V|I|M| |-| |m|a|i|n| |h|e|l|p| |f|i|l|e| @29| +0#0000000#a8a8a8255
+| +0#0000001#ffd7ff255@23|V+0#00e0e07&|I|M| |-| |m|a|i|n| |h|e|l|p| |f|i|l|e| +0#0000001&@29| +0#0000000#a8a8a8255
 | +0#0000001#ffd7ff255@72|k| +0#0000000#a8a8a8255
 | +0#0000001#ffd7ff255@5|M|o|v|e| |a|r|o|u|n|d|:| @1|U|s|e| |t|h|e| |c|u|r|s|o|r| |k|e|y|s|,| |o|r| |"|h|"| |t|o| |g|o| |l|e|f|t|,| @11|h| @1| +0#0000000#a8a8a8255
 | +0#0000001#ffd7ff255|l| @71| +0#0000000#a8a8a8255