Update the OneOrMany doctest to test serialization too #728 #1994

Job	Run time
Rustfmt (stable)	19s
clippy_check (ubuntu-latest, stable)	22s
Build and Test (ubuntu-latest, 1.65)	2m 18s
clippy_check (ubuntu-latest, nightly)	56s
Build and Test (ubuntu-latest, 1.70)	2m 3s
clippy_check (windows-latest, stable)	1m 31s
Build and Test (ubuntu-latest, 1.75)	1m 43s
clippy_check (windows-latest, nightly)	1m 34s
Build and Test (ubuntu-latest, stable)	5m 59s
Build and Test (ubuntu-latest, beta)	1m 44s
Build and Test (ubuntu-latest, nightly)	2m 12s
Build and Test (windows-latest, 1.65)	3m 11s
Build and Test (windows-latest, 1.70)	2m 44s
Build and Test (windows-latest, 1.75)	2m 48s
Build and Test (windows-latest, stable)	2m 52s
Build and Test (windows-latest, beta)	3m 44s
Build and Test (windows-latest, nightly)	3m 48s
Tests result	1s
	39m 49s

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