Add support for Pip 23.3.1. #2279

Job	Run time
Check GitHub Organization	1s
tox -e format-check,typecheck,vendor-check,package	4m 10s
./dtox.sh -e py27-pip20	15m 34s
tox -e py312-pip23_3_1	25m 8s
./dtox.sh -e py35-pip20	17m 52s
tox -e py312-pip23_3_1-integration	58m 41s
./dtox.sh -e py311-pip20	19m 13s
./dtox.sh -e py311-pip22_3_1	19m 57s
./dtox.sh -e py311-pip23_1_2	19m 34s
./dtox.sh -e py312-pip23_3_1	18m 35s
./dtox.sh -e pypy310-pip20	28m 23s
./dtox.sh -e pypy310-pip22_3_1	28m 24s
./dtox.sh -e pypy310-pip23_1_2	40m 10s
./dtox.sh -e py27-pip20-integration	20m 0s
./dtox.sh -e py37-pip22_3_1-integration	1h 16m 45s
./dtox.sh -e py37-pip23_1_2-integration	1h 17m 16s
./dtox.sh -e py311-pip20-integration	21m 24s
./dtox.sh -e py311-pip22_3_1-integration	40m 15s
./dtox.sh -e py311-pip23_1_2-integration	25m 59s
./dtox.sh -e py312-pip23_3_1-integration	36m 6s
./dtox.sh -e pypy310-pip20-integration	55m 13s
./dtox.sh -e pypy310-pip22_3_1-integration	1h 26m 24s
./dtox.sh -e pypy310-pip23_1_2-integration	49m 15s
Gather Final Status	1s
	13h 4m 20s

Provide feedback