feat: add checks and debug for sem-release

- add one more debug message
- ensure the NEXT_VERSION is not empty before proceeding to release

This contribution is part of the [FC-0012 project](https://openedx.atlassian.net/l/cp/XGS0iCcQ) which is sparked by the [Translation Infrastructure update OEP-58](https://open-edx-proposals.readthedocs.io/en/latest/architectural-decisions/oep-0058-arch-translations-management.html#specification).

.github/workflows/release.yml

@@ -1,6 +1,9 @@
 name: Release CI
 on:
   push:
+    branches:  # Create a GitHub release from `main`
+    - main
+  pull_request:  # Test the workflow without creating a release
     branches:
     - main
 
@@ -13,21 +16,36 @@ jobs:
       uses: actions/checkout@v3
       with:
         fetch-depth: 0
-    - name: semantic release
+
+    - name: Prepare semantic release
       env:
         GITHUB_TOKEN: ${{ secrets.SEMANTIC_RELEASE_GITHUB_TOKEN }}
       run: |
         # Run in dry-run mode to determine the next tag version and store it in semantic-release-next-version.txt
-        npx [email protected] --dry-run | tee semantic-release-dry-run-output.txt
-        cat semantic-release-dry-run-output.txt \
-          | grep -o 'Skip v.* tag creation in dry-run mode' \
-          | sed -e 's/^Skip //' | sed -e 's/ tag creation in dry-run mode$//' \
-          | tee semantic-release-next-version.txt
+        npx [email protected] --dry-run | tee semantic-release-next-version.txt
+
+        NEXT_VERSION=$(
+          cat semantic-release-next-version.txt | \
+            grep -o 'Skip v.* tag creation in dry-run mode' \
+            | sed -e 's/^Skip //' | sed -e 's/ tag creation in dry-run mode$//'
+        )
+
+        echo "DEBUG: Next version is '$NEXT_VERSION'"  # Debug version number
 
-        echo "DEBUG: Next version is '$(cat semantic-release-next-version.txt)'"  # Debug version number
+        if [ -z "$NEXT_VERSION" ]; then
+          echo "ERROR: Could not determine next version from semantic-release dry-run output."
+          exit 1
+        fi
 
         # Hardcode the next tag version in the atlas script
-        sed -i -e "s/_ATLAS_VERSION=.*/_ATLAS_VERSION=\"$(cat semantic-release-next-version.txt)\"  # Tagged by release.yml/" atlas
+        sed -i -e "s/_ATLAS_VERSION=.*/_ATLAS_VERSION=\"$NEXT_VERSION\"  # Tagged by release.yml/" atlas
 
+        echo "DEBUG: 'atlas --version' output is '$(./atlas --version)'"  # Debug version number
+
+    - name: Semantic release
+      env:
+        GITHUB_TOKEN: ${{ secrets.SEMANTIC_RELEASE_GITHUB_TOKEN }}
+      if: github.ref == 'refs/heads/main'
+      run: |
         # Actually create the tag and upload the atlas script
         npx [email protected]