Update soroban-dev image to use 20.0.0 versions #550

Job	Run time
amd64 / build-stellar-core	17m 48s
amd64 / build-stellar-horizon	3m 14s
amd64 / build-stellar-friendbot	49s
amd64 / build-stellar-soroban-rpc	1m 49s
amd64 / build-rs-stellar-xdr	1m 41s
arm64 / build-stellar-core	1h 17m 3s
arm64 / build-stellar-friendbot	4m 46s
arm64 / build-stellar-horizon	8m 9s
arm64 / build-rs-stellar-xdr	1m 58s
arm64 / build-stellar-soroban-rpc	3m 30s
amd64 / build	7m 26s
amd64 / test (testnet)	2m 51s
amd64 / test (testnet, --enable-soroban-rpc)	3m 30s
amd64 / test (pubnet)	1m 14s
amd64 / test (local)	1m 39s
amd64 / push-pr	0s
amd64 / test (local, --enable-soroban-rpc)	1m 44s
amd64 / push-release	0s
arm64 / build	7m 46s
arm64 / test (testnet)	18m 5s
arm64 / test (testnet, --enable-soroban-rpc)	21m 14s
arm64 / test (pubnet)	1m 14s
arm64 / push-pr	0s
arm64 / test (local)	2m 6s
arm64 / test (local, --enable-soroban-rpc)	2m 11s
arm64 / push-release	0s
manifest / push	0s
complete	1s
	3h 11m 48s

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