Convert all content types to string #791

Job	Run time
unit-tests (ubuntu-latest, v0.11.1)	31s
unit-tests (ubuntu-latest, nightly)	35s
unit-tests (windows-latest, nightly)	59s
unit-tests (macos-latest, nightly)	50s
unit-tests (windows-latest, v0.11.1)	1m 5s
unit-tests (macos-latest, v0.11.1)	49s
	4m 49s

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