Gitlab: unable to determine revision or file path

Created by: lguychard

From Sentry: https://sentry.io/organizations/sourcegraph/issues/791332306/?project=1334031&query=is%3Aunresolved+extension_version%3A19.10.9.1226+extension_version%3A19.10.9.1226&statsPeriod=14d

Seems to happen because getPageInfo() defaults to GitLabPageKind.File regardless of the URL, but getFilePageInfo() expects the URL to match a specific pattern.