replay: do not start leader for a block we already have shreds for #8588

Job	Run time
check	3m 8s
cargo-test-sbf (token/program)	8m 52s
cargo-test-sbf (instruction-padding/program, token/program-2022, token/program-2022-test)	14m 25s
test (token/cli, token/program, token/program-2022, associated-token-account/program, instruction...	20m 44s
cargo-test-sbf (associated-token-account/program, associated-token-account/program-test)	9m 0s
test (single-pool/cli, single-pool/program)	17m 35s
test (token-upgrade/cli, token-upgrade/program)	16m 0s
cargo-test-sbf (token-upgrade/program)	9m 46s
cargo-test-sbf (feature-proposal/program)	8m 32s
cargo-test-sbf (governance/addin-mock/program, governance/program)	12m 3s
cargo-test-sbf (memo/program)	7m 51s
cargo-test-sbf (name-service/program)	9m 1s
cargo-test-sbf (stake-pool/program)	14m 20s
cargo-test-sbf (single-pool/program)	9m 26s
	2h 40m 43s

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