pip cache remove for out-of-test testing of builder plugins. #2676

Job	Run time
Downstream builds with Python 3.8	36s
Python 3.8 on Linux	1m 52s
Downstream builds with Python 3.9	41s
Downstream builds with Python 3.10	1m 1s
Python 3.9 on Linux	2m 1s
Python 3.10 on Linux	2m 6s
Downstream builds with Python 3.11	34s
Python 3.11 on Linux	1m 47s
Downstream builds with Python 3.12	47s
Python 3.12 on Linux	2m 25s
Python 3.8 on Windows	4m 46s
Python 3.9 on Windows	4m 1s
Python 3.10 on Windows	4m 38s
Python 3.11 on Windows	4m 24s
Python 3.12 on Windows	4m 43s
Python 3.8 on macOS	1m 42s
Python 3.9 on macOS	1m 9s
Python 3.10 on macOS	1m 25s
Python 3.11 on macOS	1m 7s
Python 3.12 on macOS	1m 15s
Report coverage	36s
check	1s
	43m 37s

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