chore(deps): update apache/beam_python3.8_sdk docker tag to v2.29.0 (GoogleCloudPlatform#5753)

Co-authored-by: Leah E. Cole <6719667+leahecole@users.noreply.github.com>

Author: renovate-bot

dataflow/gpu-workers/Dockerfile

@@ -25,7 +25,7 @@ ARG python_version=3.8
 WORKDIR /root
 
 # Copy the Apache Beam worker files and the requirements.txt file.
-COPY --from=apache/beam_python3.8_sdk:2.28.0 /opt/apache/beam /opt/apache/beam
+COPY --from=apache/beam_python3.8_sdk:2.29.0 /opt/apache/beam /opt/apache/beam
 COPY requirements.txt .
 
 # Update PATH so we find our new Conda and Python installations.