fix: update sep5 to use newest e25519-dalek #493

Job	Run time
build (stellar-cli, stellar, ubuntu-20.04, x86_64-unknown-linux-gnu)	14m 11s
build (stellar-cli, stellar, ubuntu-20.04, aarch64-unknown-linux-gnu)	16m 34s
build (stellar-cli, stellar, macos-14, x86_64-apple-darwin)	10m 18s
build (stellar-cli, stellar, macos-12, aarch64-apple-darwin)	19m 43s
build (stellar-cli, stellar, windows-latest, x86_64-pc-windows-msvc, .exe)	20m 51s
build (soroban-cli, soroban, ubuntu-20.04, x86_64-unknown-linux-gnu)	14m 2s
build (soroban-cli, soroban, ubuntu-20.04, aarch64-unknown-linux-gnu)	16m 33s
build (soroban-cli, soroban, macos-14, x86_64-apple-darwin)	10m 37s
build (soroban-cli, soroban, macos-12, aarch64-apple-darwin)	15m 16s
build (soroban-cli, soroban, windows-latest, x86_64-pc-windows-msvc, .exe)	22m 14s
	2h 40m 19s

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