pin pandas 0.25.3

Author: wesm

ci/docker/conda-python-spark.dockerfile

@@ -22,9 +22,11 @@ FROM ${repo}:${arch}-conda-python-${python}
 
 ARG jdk=8
 ARG maven=3.5
+
+# The Spark tests currently break with pandas >= 1.0
 RUN conda install -q \
         patch \
-        pandas \
+        pandas=0.25.3 \
         openjdk=${jdk} \
         maven=${maven} && \
     conda clean --all