Use a separate GOCACHE for config and config-next #5079

Job	Run time
vendorcheck (1.21.3)	5s
govulncheck (1.21.3)	1m 0s
b (go1.21.1_2023-09-07, ./t.sh --lints --generate)	3m 6s
b (go1.21.1_2023-09-07, ./t.sh --integration && ./test/test-caa-log-checker.sh)	5m 25s
b (go1.21.1_2023-09-07, ./tn.sh --integration)	5m 45s
b (go1.21.1_2023-09-07, ./t.sh --unit --enable-race-detection)	7m 13s
b (go1.21.1_2023-09-07, ./tn.sh --unit --enable-race-detection)	8m 54s
b (go1.21.1_2023-09-07, ./t.sh --start-py)	1m 22s
b (go1.21.3_2023-10-12, ./t.sh --lints --generate)	3m 0s
b (go1.21.3_2023-10-12, ./t.sh --integration && ./test/test-caa-log-checker.sh)	6m 6s
b (go1.21.3_2023-10-12, ./tn.sh --integration)	7m 23s
b (go1.21.3_2023-10-12, ./t.sh --unit --enable-race-detection)	6m 44s
b (go1.21.3_2023-10-12, ./tn.sh --unit --enable-race-detection)	6m 53s
b (go1.21.3_2023-10-12, ./t.sh --start-py)	1m 21s
Boulder CI Test Matrix	1s
	1h 4m 18s

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