Document return type value of set_error_handler and error handler cha… #2048

Job	Run time
Run cs-fixer and stubs structure tests	2m 56s
Run tests against php 5.6	11m 30s
Run tests against php 7.0	11m 25s
Run tests against php 7.1	13m 2s
Run tests against php 7.2	13m 5s
Run tests against php 7.3	13m 44s
Run tests against php 7.4	14m 24s
Run tests against php 8.0	14m 49s
Run tests against php 8.1	15m 10s
Run tests against php 8.2	14m 42s
Run tests against php 8.3	14m 52s
	2h 19m 39s

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