Bump 1.5.0-rc.1 #751

Job	Run time
test-macos	3m 51s
test	1m 41s
test-conformance (benchmarks)	3m 30s
test-conformance (test-features)	3m 31s
test-conformance (test-conformance)	2m 51s
test-conformance (test-conformance-http)	3m 13s
test-conformance (test-conformance-nats)	3m 11s
test-conformance (test-conformance-nats-embedded)	3m 9s
test-conformance (test-conformance-ssl)	3m 13s
test-conformance (test-conformance-broker-http)	2m 34s
test-conformance (test-conformance-broker-redis)	3m 44s
test-conformance (test-conformance-broker-nats)	2m 44s
test-conformance (test-conformance-embedded)	2m 41s
coverage	6s
	39m 59s

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