Update mixer-ci image build

Rework how mixer-ci is built and remove it from the test matrix as it
is no longer automatically updated as github's runner isn't able to
build it at this time.

Signed-off-by: William Douglas <william.douglas@intel.com>

.github/workflows/test.yml

@@ -18,7 +18,6 @@ jobs:
          - machine-learning-ui
          - mariadb
          - memcached
-         - mixer-ci
          - nginx
          - node
          - openjdk/8
@@ -44,6 +43,6 @@ jobs:
       run: |
         dir=$(pwd)
         cd ${{matrix.node}}
-        docker build -t clearlinux/${{matrix.node}} .
+        docker build -t ghcr.io/clearlinux/${{matrix.node}} .
         cd $dir
         if [ -d "./tests/${{matrix.node}}" ]; then cd tests; make ${{matrix.node}}; fi