Add support of using custom env variables #3034

Job	Run time
Test Examples	17s
Test Docs	20s
Test Lint	16s
build (ubuntu-latest, 3.8)	14s
check_release	22s
Check Links	13s
build (ubuntu-latest, 3.11)	15s
build (windows-latest, 3.8)	9s
integration_check (ubuntu-latest, 3.8)	12s
build (windows-latest, 3.11)	10s
integration_check_pypy	26s
Make SDist	17s
integration_check (ubuntu-latest, 3.9)	19s
build (macos-latest, 3.8)	12s
integration_check (ubuntu-latest, 3.10)	19s
build (macos-latest, 3.11)	12s
integration_check (ubuntu-latest, 3.11)	21s
Test Minimum Versions	15s
build (windows-latest, 3.9)	9s
Test Prereleases	12s
build (ubuntu-latest, pypy-3.8)	11s
build (macos-latest, 3.10)	12s
build (ubuntu-latest, 3.12)	11s
Install from SDist and Test	1s
coverage	1s
tests_check	24s
	6m 10s

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