First a caveat. This process is obscure and not very portable, but with a fair bit of effort it can be made to work. If we are to see an easier (and better) result then either a new, purpose written object is required, OR, perhaps Linespan.nw could be modified to allow for angling the line.
It's just the accent from the same font as the lines - the system font. I selected it by opening the text dialogue, selecting "Staff Symbols" as the Display Font and using the Char Map to find something I could use as an arrow head on the end of the line, which comes from characters in the same font.
Once it was in the text entry box I copied it to the clipboard and pasted it into the objects properties dialogue.
I'm sure there are better ways, maybe find a different font that has both a well formed arrow and a line that can be connected with it more seamlessly. E.G. WebDings3 has lots of arrows, but no lines that might be added to them to extend them.
<wait a few...>
Right, Times New Roman has lines and arrows that might be able to be connected, but the arrowheads are small so enlarging the font size would help...
<wait a few more...>
OK, just tried it - I used the Windows Character map instead of the built-in NWC one to find the characters. They're pretty far down the font... The lines don't connect perfectly to the arrow shaft, but they're "near enough for jazz"
This example has the previous long arrow but moved to the left, a new arrow with a small font size (also a little to the left), and a new arrow in the original position but using a larger font size for comparison.
|SongInfo|Title:""|Author:"<Name>"|Lyricist:""|Copyright1:"Copyright © 2022 <Name>"|Copyright2:"All Rights Reserved"
|Font|Style:StaffItalic|Typeface:"Times New Roman"|Size:10|Bold:Y|Italic:Y|CharSet:0
|Font|Style:StaffBold|Typeface:"Times New Roman"|Size:8|Bold:Y|Italic:N|CharSet:0
|Font|Style:StaffLyric|Typeface:"Times New Roman"|Size:7.2|Bold:N|Italic:N|CharSet:0
|Font|Style:PageTitleText|Typeface:"Times New Roman"|Size:24|Bold:Y|Italic:N|CharSet:0
|Font|Style:PageText|Typeface:"Times New Roman"|Size:12|Bold:N|Italic:N|CharSet:0
|Font|Style:PageSmallText|Typeface:"Times New Roman"|Size:8|Bold:N|Italic:N|CharSet:0
|Font|Style:User1|Typeface:"Times New Roman"|Size:8|Bold:N|Italic:N|CharSet:1
|Font|Style:User2|Typeface:"Times New Roman"|Size:16|Bold:N|Italic:N|CharSet:1
|Font|Style:User3|Typeface:"Times New Roman"|Size:8|Bold:N|Italic:N|CharSet:0
|Font|Style:User4|Typeface:"Times New Roman"|Size:8|Bold:N|Italic:N|CharSet:0
|Font|Style:User5|Typeface:"Times New Roman"|Size:8|Bold:N|Italic:N|CharSet:0
|Font|Style:User6|Typeface:"Times New Roman"|Size:8|Bold:N|Italic:N|CharSet:0