credential-cache: handle ECONNREFUSED gracefully #5275

Job	Run time
config	5s
fuzz smoke test	36s
win build	2m 7s
static-analysis	2m 26s
sparse	2m 23s
win+VS build (arm64)	2m 13s
win+VS build (x64)	2m 8s
almalinux-8 (almalinux:8)	1m 36s
debian-11 (debian:11)	1m 38s
linux32 (i386/ubuntu:focal)	2m 11s
linux-musl (alpine)	1m 49s
pedantic (fedora)	1m 36s
documentation	2m 23s
linux-asan-ubsan (ubuntu-latest)	2m 24s
linux-gcc-default (ubuntu-latest)	1m 35s
linux-leaks (ubuntu-latest)	1m 3s
linux-gcc (ubuntu-20.04)	1m 36s
linux-reftable (ubuntu-latest)	2m 6s
linux-reftable-leaks (ubuntu-latest)	1m 0s
linux-sha256 (ubuntu-latest)	1m 46s
linux-TEST-vars (ubuntu-20.04)	1m 28s
osx-clang (macos-13)	1m 6s
osx-gcc (macos-13)	53s
osx-reftable (macos-13)	47s
win test	0s
win+VS test	0s
	38m 55s

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