Simplify example blob_05_default_credential.rs #3735

Job	Run time
test AutoRust	3m 16s
Code Style	5m 25s
Get minimum supported rust version	17s
SDK Tests (stable, false)	10m 2s
SDK Tests (1.70.0, false)	10m 8s
SDK Tests (nightly, true)	8m 18s
Services Tests (stable, false)	30m 28s
Services Tests (1.70.0, false)	25m 9s
Services Tests (nightly, true)	34m 31s
Integration Tests (stable, false)	9m 17s
Integration Tests (1.70.0, false)	10m 33s
Integration Tests (nightly, true)	7m 32s
E2E Tests (stable, false)	1m 1s
E2E Tests (1.70.0, false)	1m 3s
E2E Tests (nightly, true)	1m 2s
	2h 38m 2s

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