main/haproxy: upgrade to 2.1.8

change make TARGET to linux-musl, it is supported now
7 jobs for !12185 with 3.12-stable-haproxy-2.1.8 in 20 minutes and 48 seconds (queued for 2 seconds)
detached
Status Job ID Name Coverage
  Lint
passed #202028
x86_64 docker-alpine
lint

00:02:17

 
  Build
passed #202033
aarch64 ci-build docker-alpine
build-aarch64

00:05:13

passed #202034
armv7 ci-build docker-alpine
build-armv7

00:07:47

passed #202032
ppc64le ci-build docker-alpine
build-ppc64le

00:10:42

passed #202031
s390x ci-build docker-alpine
build-s390x

00:01:19

passed #202030
x86 ci-build docker-alpine
build-x86

00:01:36

passed #202029
x86_64 ci-build docker-alpine
build-x86_64

00:01:32