calculate ancient slot boundary correctly for hash calc #8517

Job	Run time
check	3m 8s
test (token/cli, token/program, token/program-2022, associated-token-account/program, instruction...	20m 45s
cargo-test-sbf (token/program)	9m 15s
test (single-pool/cli, single-pool/program)	19m 26s
test (token-upgrade/cli, token-upgrade/program)	17m 45s
cargo-test-sbf (instruction-padding/program, token/program-2022, token/program-2022-test)	15m 50s
cargo-test-sbf (associated-token-account/program, associated-token-account/program-test)	11m 57s
cargo-test-sbf (token-upgrade/program)	9m 21s
cargo-test-sbf (feature-proposal/program)	8m 51s
cargo-test-sbf (governance/addin-mock/program, governance/program)	15m 27s
cargo-test-sbf (memo/program)	9m 55s
cargo-test-sbf (name-service/program)	10m 11s
cargo-test-sbf (stake-pool/program)	12m 28s
cargo-test-sbf (single-pool/program)	11m 11s
	2h 55m 30s

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