Fix misaligned store in `Bool` to union upcasts #12103

Job	Run time
check_format	1m 33s
deploy_api_docs	0s
x86_64-gnu-test (1.7.3)	34m 37s
x86_64-gnu-test (1.8.2)	32m 24s
x86_64-gnu-test-preview_mt	5m 39s
x86_64-musl-test	37m 7s
x86_64-gnu-test (1.9.2)	35m 11s
x86_64-gnu-test (1.10.1)	35m 27s
x86_64-gnu-test (1.11.2)	32m 37s
x86_64-gnu-test (1.12.2)	33m 1s
x86_64-gnu-test (1.13.1)	34m 28s
x86_64-gnu-test (1.0.0, FLAGS=-Dwithout_ffi USE_PCRE1=true)	32m 58s
x86_64-gnu-test (1.1.1, FLAGS=-Dwithout_ffi USE_PCRE1=true)	34m 31s
x86_64-gnu-test (1.2.2, USE_PCRE1=true)	35m 23s
x86_64-gnu-test (1.3.2, USE_PCRE1=true)	32m 28s
x86_64-gnu-test (1.4.1, USE_PCRE1=true)	36m 0s
x86_64-gnu-test (1.5.1, USE_PCRE1=true)	33m 6s
x86_64-gnu-test (1.6.2, USE_PCRE1=true)	33m 9s
	8h 39m 39s

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