Avoid --find-links in wheel jobs (#4509)

Contributes to rapidsai/build-planning#69
Contributes to rapidsai/build-planning#33

Proposes a stricter pattern for passing a `pylibcugraph` wheel from the `wheel-build-cpp` job that produced it into the `wheel-build-python` job wanting to use it (as a build dependency of `cugraph`). This change improves the likelihood that issues with the `pylibcugraph` wheels will be caught in CI.

## Notes for Reviewers

See rapidsai/rmm#1586 and rapidsai/build-planning#69 (comment) for details on how I tested this approach.

Authors:
  - James Lamb (https://github.com/jameslamb)

Approvers:
  - Mike Sarahan (https://github.com/msarahan)

URL: #4509

ci/build_wheel_cugraph.sh

@@ -6,11 +6,16 @@ set -euo pipefail
 RAPIDS_PY_CUDA_SUFFIX="$(rapids-wheel-ctk-name-gen ${RAPIDS_CUDA_VERSION})"
 
 # Download the pylibcugraph wheel built in the previous step and make it
-# available for pip to find. We must use PIP_FIND_LINKS because the package
-# must be made available to the isolated build step, and there is no way to
-# manually install it into that environment.
-RAPIDS_PY_WHEEL_NAME=pylibcugraph_${RAPIDS_PY_CUDA_SUFFIX} rapids-download-wheels-from-s3 ./local-pylibcugraph
-export PIP_FIND_LINKS=$(pwd)/local-pylibcugraph
+# available for pip to find.
+#
+# ensure 'cugraph' wheel builds always use the 'pylibcugraph' just built in the same CI run
+#
+# using env variable PIP_CONSTRAINT is necessary to ensure the constraints
+# are used when creating the isolated build environment
+CPP_WHEELHOUSE=$(RAPIDS_PY_WHEEL_NAME="pylibcugraph_${RAPIDS_PY_CUDA_SUFFIX}" rapids-download-wheels-from-s3 /tmp/pylibcugraph_dist)
+
+echo "pylibcugraph-${RAPIDS_PY_CUDA_SUFFIX} @ file://$(echo ${CPP_WHEELHOUSE}/pylibcugraph_*.whl)" > ./constraints.txt
+export PIP_CONSTRAINT="${PWD}/constraints.txt"
 
 PARALLEL_LEVEL=$(python -c \
   "from math import ceil; from multiprocessing import cpu_count; print(ceil(cpu_count()/4))")