Make `html5ever` compilable on beta #4700

Job	Run time
Test and deploy	1m 42s
Test on Windows	2m 20s
Test benchmarks (--include cargo-0.87.1,stm32f4-0.15.1, Opt)	6m 50s
Test benchmarks (--exclude cargo-0.87.1,stm32f4-0.15.1, Opt)	11m 16s
Test benchmarks (--include cargo-0.87.1,stm32f4-0.15.1, Check,Debug,Doc)	6m 12s
Test benchmarks (--exclude cargo-0.87.1,stm32f4-0.15.1, Check,Debug,Doc)	12m 1s
docker	1m 59s
Test codegen backend benchmarks	1m 9s
Database Check	1m 20s
Test runtime benchmarks	4m 31s
Test profiling	4m 6s
Compare page endpoint test	6m 22s
conclusion	2s
	59m 50s

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