Fix otel docker image build when running on a tagged pipeline (#35390)

Author: Pythyu

.gitlab/integration_test/otel.yml

@@ -37,7 +37,7 @@ docker_image_build_otel:
       "github.com/open-telemetry/opentelemetry-collector-contrib/processor/metricstransformprocessor ${OTELCOL_VERSION}"
   script:
     - !reference [.login_to_docker_readonly]
-    - docker build --build-arg AGENT_BRANCH=$CI_COMMIT_BRANCH --tag agent-byoc:latest -f /tmp/otel-ci/Dockerfile.agent-otel /tmp/otel-ci
+    - docker build --build-arg AGENT_BRANCH=$CI_COMMIT_REF_NAME --tag agent-byoc:latest -f /tmp/otel-ci/Dockerfile.agent-otel /tmp/otel-ci
     - OT_AGENT_IMAGE_NAME=agent-byoc OT_AGENT_TAG=latest python3 /tmp/otel-ci/otel_agent_build_tests.py
   rules:
     - !reference [.except_mergequeue]