Be less restrictive on what characters are disallowed in custom slugs #1604

Job	Run time
static-analysis (8.3, cs)	43s
static-analysis (8.3, stan)	31s
static-analysis (8.3, openapi:validate)	22s
unit-tests / tests (8.3)	1m 5s
cli-tests / tests (8.3)	1m 32s
unit-tests / tests (8.4)	27s
api-tests / tests (8.3)	1m 17s
cli-tests / tests (8.4)	47s
api-tests / tests (8.4)	1m 23s
db-tests (maria) / db-tests (8.3)	23s
db-tests (maria) / db-tests (8.4)	34s
db-tests (mysql) / db-tests (8.3)	32s
db-tests (mysql) / db-tests (8.4)	40s
db-tests (ms) / db-tests (8.3)	2m 1s
db-tests (postgres) / db-tests (8.3)	27s
db-tests (postgres) / db-tests (8.4)	30s
db-tests (ms) / db-tests (8.4)	52s
db-tests (sqlite:ci) / db-tests (8.3)	30s
db-tests (sqlite:ci) / db-tests (8.4)	17s
upload-coverage (8.3)	20s
delete-artifacts	4s
	15m 17s

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