bump github.com/prometheus/client_golang to v1.20.5 #3777

Job	Run time
Basic Checks	3m 10s
Integration Tests (raft)	12m 31s
Integration Tests (pvtdata)	12m 19s
Unit Tests	15m 5s
Integration Tests (pvtdatapurge e2e)	10m 57s
Integration Tests (ledger)	13m 37s
Integration Tests (lifecycle)	6m 35s
Integration Tests (smartbft)	19m 51s
Integration Tests (discovery gossip devmode pluggable)	6m 32s
Integration Tests (gateway idemix pkcs11 configtx configtxlator)	17m 16s
Integration Tests (sbe nwo msp)	8m 0s
	2h 5m 53s

Provide feedback