Update soroban-dev image to use 20.0.0 versions #547

Job	Run time
amd64 / build-rs-stellar-xdr	2m 0s
amd64 / build-stellar-core	27s
amd64 / build-stellar-horizon	2m 12s
amd64 / build-stellar-friendbot	41s
amd64 / build-stellar-soroban-rpc	45s
arm64 / build-rs-stellar-xdr	58m 58s
arm64 / build-stellar-core	37s
arm64 / build-stellar-friendbot	2m 6s
arm64 / build-stellar-horizon	7m 18s
arm64 / build-stellar-soroban-rpc	45s
amd64 / build	3m 18s
amd64 / test (pubnet)	1m 18s
amd64 / test (local)	1m 34s
amd64 / push-pr	0s
amd64 / push-release	0s
arm64 / build	6m 40s
arm64 / test (pubnet)	1m 12s
arm64 / test (local)	2m 12s
arm64 / push-pr	0s
arm64 / push-release	0s
manifest / push	0s
complete	1s
	1h 32m 4s

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