fix(node): fix update-config when reward.conf does not exist #22550

Job	Run time
Bazel Test All	14m 47s
Bazel Build All Config Check	0s
Bazel Build Fuzzers AFL	4m 30s
Bazel Build Fuzzers	2m 24s
Bazel Test macOS Intel	0s
Build IC	10m 38s
Cargo Build Release Linux	7m 40s
Python CI Tests	1m 35s
Cargo Clippy Linux	3m 56s
Build Determinism (//publish/binaries:upload, release, build-ic/release, false)	22s
Build Determinism (//publish/canisters:upload, canisters, build-ic/canisters, false)	18s
Build Determinism (//ic-os/guestos/envs/prod:upload_disk-img, guest-os/update-img, build-ic/icos/...	20s
Build Determinism (//ic-os/hostos/envs/prod:upload_update-img, host-os/update-img, build-ic/icos/...	19s
Build Determinism (//ic-os/setupos/envs/prod:upload_disk-img, setup-os/disk-img, build-ic/icos/se...	19s
	47m 8s

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