devel/cgit: Fix fetch

yasu@rolling-vm-freebsd2[1018]% pwd
/usr/ports/devel/cgit
yasu@rolling-vm-freebsd2[1019]% make fetch
===>  License GPLv2 accepted by the user
===>   cgit-1.2.3 depends on file: /usr/local/sbin/pkg - found
=> cgit-1.2.3.tar.xz doesn't seem to exist in /net/freebsd/ports/distfiles/.
=> Attempting to fetch http://git.zx2c4.com/cgit/snapshot/cgit-1.2.3.tar.xz
fetch: http://git.zx2c4.com/cgit/snapshot/cgit-1.2.3.tar.xz: size unknown
fetch: http://git.zx2c4.com/cgit/snapshot/cgit-1.2.3.tar.xz: size of remote file is not known
cgit-1.2.3.tar.xz                                       88 kB  353 kBps    00s
=> git-2.25.1.tar.xz doesn't seem to exist in /net/freebsd/ports/distfiles/.
===> /!\ Error /!\
     The :git group used for git-2.25.1.tar.xz is missing
     from MASTER_SITES. Check for typos, or errors.
*** Error code 1

Stop.
make: stopped in /usr/ports/devel/cgit
yasu@rolling-vm-freebsd2[1020]%

Approved by:	portmgr blanket (just fix it)
MFH:		2023Q2