Update web workflow with additional logic (#3256)

Co-authored-by: Joseph Flinn <58369717+joseph-flinn@users.noreply.github.com>

.github/workflows/build-web.yml

@@ -341,12 +341,18 @@ jobs:
       - name: Get image tag
         id: image-tag
         run: |
+          if [[ $(grep "pull" <<< "${GITHUB_REF}") ]]; then
+            IMAGE_TAG=${GITHUB_HEAD_REF}
+          else
             IMAGE_TAG=$(echo "${GITHUB_REF:11}" | sed "s#/#-#g")
+          fi
+
           TAG_EXTENSION=${{ github.event.inputs.custom_tag_extension }}
 
           if [[ $TAG_EXTENSION ]]; then
             IMAGE_TAG=$IMAGE_TAG-$TAG_EXTENSION
           fi
+
           echo "::set-output name=value::$IMAGE_TAG"
 
       - name: Tag image