fail loudly on unsized by-ref invariants #4419

Job	Run time
bench	5m 32s
todo_check	23s
rustfmt	13s
test_llvm	4m 3s
dist (macos-latest, aarch64-apple-darwin)	1m 32s
dist (windows-latest, x86_64-pc-windows-msvc)	2m 12s
dist (macos-15-intel, x86_64-apple-darwin)	4m 27s
dist (windows-latest, x86_64-pc-windows-gnu)	3m 0s
test (macos-latest, aarch64-apple-darwin)	10m 55s
test (ubuntu-24.04-arm, aarch64-unknown-linux-gnu)	8m 59s
test (ubuntu-latest, s390x-unknown-linux-gnu, gcc-s390x-linux-gnu qemu-user)	4m 6s
dist (ubuntu-22.04, x86_64-unknown-linux-gnu)	1m 42s
dist (ubuntu-24.04-arm, aarch64-unknown-linux-gnu)	1m 45s
test (macos-15-intel, x86_64-apple-darwin)	25m 22s
test (ubuntu-latest, x86_64-unknown-linux-gnu)	12m 1s
test (ubuntu-latest, riscv64gc-unknown-linux-gnu, gcc-riscv64-linux-gnu qemu-user)	4m 3s
test (windows-latest, x86_64-pc-windows-gnu)	21m 57s
test (windows-latest, x86_64-pc-windows-msvc)	16m 15s
release	0s
	2h 8m 27s

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