fix(ct): base image build matrix output must be on a single line

Fix jq output by removing newlines and superfluous whitespace.

.github/workflows/container_base_push.yml

@@ -35,7 +35,9 @@ jobs:
               run: |
                   # Get last three releases and include develop branch as matrix elements
                   #if [[ "${{ github.event_name }}" == "schedule" ]]; then
-                    echo "branches=$(curl -f -sS https://api.github.com/repos/IQSS/dataverse/releases | jq '[ .[0:3] | .[].tag_name, "develop" ]')" | tee -a "$GITHUB_OUTPUT"
+                    echo "branches=$(curl -f -sS https://api.github.com/repos/IQSS/dataverse/releases | \
+                    jq '[ .[0:3] | .[].tag_name, "develop" ]')" | tr -d "\n" | tr -s " " | \
+                    tee -a "$GITHUB_OUTPUT"
                   #else
                   #  echo "branches=['develop']" | tee -a "$GITHUB_OUTPUT"
                   #fi