Bump express from 4.19.2 to 4.21.0 #587

Job	Run time
CI / Generate matrix	12s
CI / Context	1s
CI / Check governance	1s
CI / 8.1 prf-low mysql57 phpunit all	1m 2s
CI / 8.2 mariadb phpunit all	1m 46s
CI / 8.3 mysql80 phpunit all	1m 30s
CI / 8.1 mysql57 phplinting	1m 1s
CI / 8.1 mysql57 endtoend root job1	2m 5s
CI / 8.3 mysql80 endtoend root job1	2m 6s
CI / 8.1 mysql57 endtoend root job2	2m 46s
CI / 8.3 mysql80 endtoend root job2	2m 13s
CI / 8.1 mysql57 js	1m 4s
CI / Dispatch tag patch release	0s
	15m 47s

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