Fix BankForks::new_rw_arc memory leak #7140

Job	Run time
check	3m 42s
cargo-test-sbf (token/program)	8m 52s
test (token/cli, token/program, token/program-2022, associated-token-account/program, instruction...	19m 40s
cargo-test-sbf (instruction-padding/program, token/program-2022, token/program-2022-test)	16m 46s
test (single-pool/cli, single-pool/program)	21m 1s
cargo-test-sbf (associated-token-account/program, associated-token-account/program-test)	9m 24s
test (token-upgrade/cli, token-upgrade/program)	19m 38s
cargo-test-sbf (token-upgrade/program)	9m 7s
cargo-test-sbf (feature-proposal/program)	13m 50s
cargo-test-sbf (governance/addin-mock/program, governance/program)	12m 25s
cargo-test-sbf (memo/program)	8m 55s
cargo-test-sbf (name-service/program)	9m 30s
cargo-test-sbf (stake-pool/program)	14m 14s
cargo-test-sbf (single-pool/program)	10m 0s
	2h 57m 4s

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