Fix DDS Router branch selection in push-to-main runs (#451)

Signed-off-by: Raul Sanchez-Mateos <raul@eprosima.com>

Author: rsanchez15

.github/workflows/test.yml

@@ -75,7 +75,7 @@ jobs:
       fastdds_branch: ${{ inputs.fastdds_branch || '2.x' }}
       dev_utils_branch: ${{ inputs.dev_utils_branch || 'main' }}
       ddspipe_branch: ${{ inputs.ddspipe_branch || 'main' }}
-      ddsrouter_branch: ${{ inputs.ddsrouter_branch || github.head_ref }}
+      ddsrouter_branch: ${{ inputs.ddsrouter_branch || github.head_ref || github.ref_name }}
       custom_version_build: ${{ inputs.custom_version_build || 'v2' }}
       dependencies_artifact_postfix: ${{ inputs.dependencies_artifact_postfix || '_nightly' }}
     secrets: inherit