(actions) use brackets for env vars (#32)

Author: MatthijsBurgh

.github/workflows/main.yml

@@ -36,7 +36,7 @@ jobs:
           BRANCH=${GITHUB_BASE_REF:-${GITHUB_REF}}
           mkdir -p ${HOME}/.ssh
           ssh-keyscan -t rsa -H "github.com" 2>&1 | tee -a "${HOME}"/.ssh/known_hosts
-          .ci/install.bash --branch=$BRANCH --sl=ed --sl=geolib2 --sl=rgbd # (In)direct deps of ed_object_models, but we don't need to build it
+          .ci/install.bash --branch=${BRANCH} --sl=ed --sl=geolib2 --sl=rgbd # (In)direct deps of ed_object_models, but we don't need to build it
       - name: Script
         run: .ci/script.bash
       - name: Before Deploy