Limit output of pytest durations

Durations output were previously increased to show all tests to allow us
debugging of timeouts. However, now they have not been as important so
limiting to only the 50 longer running tests is best to decrease log
lengths, we may soon remove it entirely if they are not currently
important.

ci/test_python.sh

@@ -52,7 +52,7 @@ UCX_WARN_UNUSED_ENV_VARS=n \
 UCX_MEMTYPE_CACHE=n \
 timeout 60m pytest \
   -vv \
-  --durations=0 \
+  --durations=50 \
   --capture=no \
   --cache-clear \
   --junitxml="${RAPIDS_TESTS_DIR}/junit-dask-cuda.xml" \
@@ -73,7 +73,7 @@ UCX_WARN_UNUSED_ENV_VARS=n \
 UCX_MEMTYPE_CACHE=n \
 timeout 30m pytest \
   -vv \
-  --durations=0 \
+  --durations=50 \
   --capture=no \
   --cache-clear \
   --junitxml="${RAPIDS_TESTS_DIR}/junit-dask-cuda-legacy.xml" \