Loosen \Drupal\entity_usage\UrlToEntityInterface::ENTITY_ROUTE_PATTERN regex

Alex Pottrequested to merge
issue/entity_usage-3603250:3603250-drupalentityusageurltoentityinterfaceentityroutepattern-does-not-2.x into 8.x-2.x

(cherry picked from commit ce42684d)

Closes #3603250

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