Change workflow to use branch name for docker tag

This is done for two reasons:

1. To more clearly distinguish the digest from the tag (the former is useful for caching, the latter is not)
2. Using the digest as a tag is overkill, as we only need to keep the newest image for each branch (that way, the docker image follows the HEAD of the branch)

Author: Potherca

.github/workflows/ci.yml

@@ -41,12 +41,12 @@ jobs:
       - name: Build Solid-Nextcloud Docker image
         run: |
           docker build \
-            --tag "solid-nextcloud:${{ github.sha }}" \
-            --tag "ghcr.io/pdsinterop/solid-nextcloud:${{ github.sha }}" \
+            --tag "solid-nextcloud:${{ github.ref_name }}" \
+            --tag "ghcr.io/pdsinterop/solid-nextcloud:${{ github.ref_name }}" \
           .
-          docker push "ghcr.io/pdsinterop/solid-nextcloud:${{ github.sha }}"
+          docker push "ghcr.io/pdsinterop/solid-nextcloud:${{ github.ref_name }}"
           mkdir -p cache/solid-nextcloud
-          docker image save solid-nextcloud:${{ github.sha }} --output ./cache/solid-nextcloud/${{ github.sha }}.tar
+          docker image save solid-nextcloud:${{ github.ref_name }} --output ./cache/solid-nextcloud/${{ github.sha }}.tar
 
   solid-testsuite:
     strategy:
@@ -95,8 +95,8 @@ jobs:
             "ghcr.io/pdsinterop/php-solid-pubsub-server:${{ env.PUBSUB_TAG }}"
 
           source ./run-solid-test-suite.sh
-          startSolidNextcloud 'server' "solid-nextcloud:${{ github.sha }}" ${{ matrix.test }}
-          startSolidNextcloud 'thirdparty' "solid-nextcloud:${{ github.sha }}" ${{ matrix.test }}
+          startSolidNextcloud 'server' "solid-nextcloud:${{ github.ref_name }}" ${{ matrix.test }}
+          startSolidNextcloud 'thirdparty' "solid-nextcloud:${{ github.ref_name }}" ${{ matrix.test }}
 
           echo "COOKIE_server=${COOKIE_server}" >> "${GITHUB_ENV}"
           echo "COOKIE_thirdparty=${COOKIE_thirdparty}" >> "${GITHUB_ENV}"