update workflows to pin python-3.12 when installing conda-build #386

Job	Run time
build_windows (3.9)	19m 25s
build_windows (3.10)	17m 38s
build_windows (3.11)	10m 47s
build_windows (3.12)	19m 24s
build_linux (3.9)	3m 14s
build_linux (3.10)	3m 21s
build_linux (3.11)	2m 33s
build_linux (3.12)	2m 38s
test_linux (3.9, false, ubuntu-latest)	1m 36s
test_linux (3.10, false, ubuntu-latest)	1m 40s
test_linux (3.11, false, ubuntu-latest)	1m 16s
test_linux (3.12, false, ubuntu-latest)	1m 10s
test_windows (3.9, false, windows-2019)	5s
test_windows (3.10, false, windows-2019)	3s
test_windows (3.11, false, windows-2019)	4s
test_windows (3.12, false, windows-2019)	4s
	1h 24m 58s

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