bump github.com/prometheus/client_golang to v1.20.5 (release-2.5) #3800

Job	Run time
Basic Checks	3m 16s
Integration Tests (raft)	13m 16s
Integration Tests (pvtdata)	14m 56s
Integration Tests (pvtdatapurge)	4m 42s
Integration Tests (ledger)	14m 58s
Unit Tests	7m 46s
Integration Tests (lifecycle)	11m 11s
Integration Tests (e2e)	7m 22s
Integration Tests (discovery gossip devmode pluggable)	8m 43s
Integration Tests (gateway idemix pkcs11 configtx configtxlator)	7m 35s
Integration Tests (sbe nwo msp)	9m 13s
	1h 42m 58s

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