GitHub Actions: clearly disable the docker build tasks

These haven't been used for a while and still create strange errors.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

.github/workflows/linux-dockerimage.disabled

@@ -0,0 +1,39 @@
+name: Linux Qt 5.12 Docker Image CI
+
+#on:
+#  push:
+#    paths:
+#    - scripts/docker/trusty-qt512/Dockerfile
+#    - .github/workflows/linux-docker*
+
+jobs:
+  trusty-qt512:
+    runs-on: ubuntu-latest
+    env:
+      VERSION: ${{ '1.0' }}    # 'official' images should have a dot-zero version
+
+    steps:
+    - uses: actions/checkout@v1
+
+    - name: Get our pre-reqs
+      run: |
+        cd scripts/docker/trusty-qt512
+        bash getpackages.sh
+
+    - name: set env
+      run: |
+        v=${{ env.VERSION }}
+        b=${{ github.ref }} # -BRANCH suffix, unless the branch is master
+        b=${b/refs\/heads\//}
+        b=${b,,} # the name needs to be all lower case
+        if [ $b = "master" ] ; then b="" ; else b="-$b" ; fi
+        echo "::set-env name=NAME::subsurface/trusty-qt512${b}:${v}"
+
+    - name: Build and Publish Linux Docker image to Dockerhub
+      uses: elgohr/Publish-Docker-Github-Action@master
+      with:
+        name:       ${{ env.NAME }}
+        username:   ${{ secrets.DOCKER_USERNAME }}
+        password:   ${{ secrets.DOCKER_PASSWORD }}
+        dockerfile: 'Dockerfile'
+        workdir:    './scripts/docker/trusty-qt512/'