Be less restrictive on what characters are disallowed in custom slugs #1603

Job	Run time
static-analysis (8.3, cs)	37s
static-analysis (8.3, stan)	38s
static-analysis (8.3, openapi:validate)	32s
api-tests / tests (8.3)	1m 19s
cli-tests / tests (8.3)	36s
unit-tests / tests (8.3)	28s
cli-tests / tests (8.4)	36s
api-tests / tests (8.4)	1m 24s
unit-tests / tests (8.4)	27s
db-tests (maria) / db-tests (8.3)	39s
db-tests (maria) / db-tests (8.4)	39s
db-tests (ms) / db-tests (8.3)	1m 1s
db-tests (mysql) / db-tests (8.3)	39s
db-tests (ms) / db-tests (8.4)	1m 0s
db-tests (mysql) / db-tests (8.4)	33s
db-tests (postgres) / db-tests (8.3)	35s
db-tests (postgres) / db-tests (8.4)	25s
db-tests (sqlite:ci) / db-tests (8.3)	30s
db-tests (sqlite:ci) / db-tests (8.4)	28s
upload-coverage (8.3)	49s
delete-artifacts	4s
	13m 59s

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