Change bash variable detection

.github/workflows/regress.yml

@@ -12,8 +12,6 @@ jobs:
       uses: actions/checkout@v4
     - name: Setup apptainer
       uses: eWaterCycle/[email protected]
-    - name: Read container tag
-      run: echo "CONTAINER_TAG=$(cat bin/.container-tag)" >> $GITHUB_ENV
     - name: Get container from cache
       id: cache-sif
       uses: actions/cache@v3

bin/setup

@@ -6,7 +6,7 @@ cd $ROOT
 
 CONTAINER_TAG=`cat ${ROOT}/bin/.container-tag`
 
-if [ -z ${GITHUB_ACTIONS+x} ]; then
+if [ -v GITHUB_ACTIONS ]; then
   CONTAINER_PATH=${ROOT}/.singularity/image-$CONTAINER_TAG.sif
   SINGULARITY_CACHE=--disable-cache
 else