Bump core in local Makefile to 20.1.0 #594

Job	Run time
amd64 / build-rs-stellar-xdr	1m 41s
amd64 / build-stellar-core	43s
amd64 / build-stellar-friendbot	53s
amd64 / build-stellar-horizon	3m 7s
amd64 / build-stellar-soroban-rpc	2m 48s
arm64 / build-rs-stellar-xdr	3m 34s
arm64 / build-stellar-friendbot	4m 41s
arm64 / build-stellar-core	20s
arm64 / build-stellar-horizon	7m 48s
arm64 / build-stellar-soroban-rpc	2m 0s
amd64 / build	5m 17s
arm64 / build	46s
amd64 / test (pubnet)	6s
amd64 / test (local)	4s
amd64 / test (local, --enable-soroban-rpc)	3s
amd64 / push-pr	0s
arm64 / push-pr	1s
arm64 / test	1s
arm64 / push-release	1s
amd64 / push-release	1s
manifest	1s
complete	1s
	33m 57s

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