Change CI to get the proper branch

Signed-off-by: laura-eprosima <laura@eprosima.com>

Author: laura-eprosima

.github/workflows/ci.yml

@@ -30,6 +30,6 @@ jobs:
 
       - name: Build and test the documentation
         run: |
-            READTHEDOCS=True sphinx-build -b html -d build/doctrees docs build/html
-            READTHEDOCS=True doc8 --max-line-length 200 docs
-            READTHEDOCS=True sphinx-build -W --keep-going -b spelling -d build/doctrees docs build/spelling
+            READTHEDOCS=True IS_BRANCH=${{ github.head_ref }} sphinx-build -b html -d build/doctrees docs build/html
+            READTHEDOCS=True IS_BRANCH=${{ github.head_ref }} doc8 --max-line-length 200 docs
+            READTHEDOCS=True IS_BRANCH=${{ github.head_ref }} sphinx-build -W --keep-going -b spelling -d build/doctrees docs build/spelling