Fix changes detection

Signed-off-by: Andreas Heinrich <andreas.heinrich@rwth-aachen.de>

.github/workflows/deploy-single-docker-image.yml

@@ -137,15 +137,18 @@ jobs:
       id: check
       run: |
         echo "Checking for changes in paths ${{ steps.setup-regex.outputs.regex }}.."
-        changed_files="$(git diff --name-only ${{ inputs.github_ref_before }} ${{ inputs.github_ref_after }} | grep -E '${{ steps.setup-regex.outputs.regex }}')"
-        changed_files_count=$(echo "$changed_files" | wc -l)
-        if [ $changed_files_count -gt 0 ]; then
+        changed_files="$(git diff --name-only ${{ inputs.github_ref_before }} ${{ inputs.github_ref_after }} | grep -E '${{ steps.setup-regex.outputs.regex }}')" || EXIT_CODE=$?
+        if [ "$EXIT_CODE" -eq "1" ]; then
+          echo "No changes detected in ${{ steps.setup-regex.outputs.regex }}!🔍"
+          echo "changes_detected=false" >> $GITHUB_OUTPUT
+          exit 0
+        elif [ "$EXIT_CODE" -ne "0" ]; then
+          echo "Error while checking for changes in ${{ steps.setup-regex.outputs.regex }}!❌"
+          exit $EXIT_CODE
+        else
           echo "🔍 Changes detected with regex ${{ steps.setup-regex.outputs.regex }} in the following files:"
           echo "$changed_files"
           echo "changes_detected=true" >> $GITHUB_OUTPUT
-        else
-          echo "No changes detected in ${{ steps.setup-regex.outputs.regex }}!🔍"
-          echo "changes_detected=false" >> $GITHUB_OUTPUT
         fi
       working-directory: source
     - name: Set outputs