Help needed with USE_GITHUB

Hi everyone,

I'm working on a port for the Gingko library 
(https://github.com/ginkgo-project/ginkgo). Since the project is hosted 
on GitHub, I'd like to make use of the USE_GITHUB macro and its friends. 
Alas, I'm not able to get it to work:

$ make makesum
===>  License BSD3CLAUSE accepted by the user
===>  License BSD3CLAUSE accepted by the user
===>   gingko-1.4.0 depends on file: /usr/local/sbin/pkg - found
=> gingko-project-gingko-v1.4.0_GH0.tar.gz doesn't seem to exist in 
/home/pj/FreeBSD/ports-wip/distfiles/.
=> Attempting to fetch 
https://codeload.github.com/gingko-project/gingko/tar.gz/v1.4.0?dummy=/gingko-project-gingko-v1.4.0_GH0.tar.gz
fetch: 
https://codeload.github.com/gingko-project/gingko/tar.gz/v1.4.0?dummy=/gingko-project-gingko-v1.4.0_GH0.tar.gz: 
Not Found
=> Attempting to fetch 
http://distcache.FreeBSD.org/ports-distfiles/gingko-project-gingko-v1.4.0_GH0.tar.gz
fetch: 
http://distcache.FreeBSD.org/ports-distfiles/gingko-project-gingko-v1.4.0_GH0.tar.gz: 
Not Found
=> Couldn't fetch it - please try to retrieve this
=> port manually into /home/pj/FreeBSD/ports-wip/distfiles/ and try again.
*** Error code 1

Stop.
make[1]: stopped in /home/pj/FreeBSD/ports-wip/math/gingko
*** Error code 1

Stop.
make: stopped in /home/pj/FreeBSD/ports-wip/math/gingko
$

Here's my WIP Makefile so far:

--------8<--------
PORTNAME=       gingko
DISTVERSIONPREFIX=      v
DISTVERSION=    1.4.0
CATEGORIES=     math
#MASTER_SITES=  GH/${GH_ACCOUNT}/${PORTNAME}/archive/refs/tags

MAINTAINER=     bsd@philippost.de
COMMENT=        High-performance linear algebra library for manycore systems

LICENSE=        BSD3CLAUSE
LICENSE_FILE=   ${WRKSRC}/LICENSE

USE_GITHUB=     yes
GH_ACCOUNT=     gingko-project

.include <bsd.port.mk>
-------->8--------

I don't understand why this fails. Looking at other ports which make use 
of USE_GITHUB (i.e., devel/mold), I fail to see what I miss.
Fetching 
https://github.com/ginkgo-project/ginkgo/archive/refs/tags/v1.4.0.tar.gz 
succeeds, hence my attempt at overriding MASTER_SITES.
When downloading the release sources using Firefox, I receive a file 
gingko-1.4.0.tar.gz. I don't know where that ultimately originates from.

What am I missing? Could someone please be so kind and enlighten me?

Philipp