chore: add more test for serde string #72

Job	Run time
doc	14s
fmt	5s
minimal-versions	17s
build (stable, dev, ubuntu-latest)	23s
build (stable, dev, ubuntu-latest, --all-features)	2m 43s
build (stable, dev, windows-latest)	2m 33s
build (stable, dev, windows-latest, --all-features)	1m 48s
build (stable, dev, macos-latest)	42s
build (stable, dev, macos-latest, --all-features)	50s
build (stable, release, ubuntu-latest)	17s
build (stable, release, ubuntu-latest, --all-features)	23s
build (stable, release, windows-latest)	1m 48s
build (stable, release, windows-latest, --all-features)	2m 9s
build (stable, release, macos-latest)	58s
build (stable, release, macos-latest, --all-features)	55s
build (nightly, dev, ubuntu-latest)	27s
build (nightly, dev, ubuntu-latest, --all-features)	28s
build (nightly, dev, windows-latest)	57s
build (nightly, dev, windows-latest, --all-features)	1m 1s
build (nightly, dev, macos-latest)	55s
build (nightly, dev, macos-latest, --all-features)	59s
build (nightly, release, ubuntu-latest)	26s
build (nightly, release, ubuntu-latest, --all-features)	31s
build (nightly, release, windows-latest)	1m 5s
build (nightly, release, windows-latest, --all-features)	1m 7s
build (nightly, release, macos-latest)	1m 8s
build (nightly, release, macos-latest, --all-features)	1m 3s
msrv	2m 32s
	28m 44s

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