testing/xmrig: upgrade to 6.8.0

Ref https://github.com/xmrig/xmrig/releases/tag/v6.8.0
7 jobs for !17484 with xmrig in 1 minute and 26 seconds
detached
Status Job ID Name Coverage
  Lint
passed #305491
docker-alpine x86_64
lint

00:00:18

 
  Build
passed #305496
docker-alpine ci-build aarch64
build-aarch64

00:01:07

passed #305497
docker-alpine ci-build armv7
build-armv7

00:00:34

passed #305495
docker-alpine ci-build ppc64le
build-ppc64le

00:00:43

passed #305494
docker-alpine ci-build s390x
build-s390x

00:00:47

passed #305493
docker-alpine ci-build x86
build-x86

00:00:59

passed #305492
docker-alpine ci-build x86_64
build-x86_64

00:00:48