fix: WS URL creation for different instance URLs

mentioned in commit bcb6d0b7

mentioned in merge request gitlab-org/workspaces/gitlab-workspaces-tools!12 (closed)

mentioned in merge request gitlab-org/workspaces/gitlab-workspaces-tools!26 (merged)

mentioned in merge request gitlab-org/workspaces/gitlab-workspaces-tools!28 (closed)

mentioned in merge request gitlab-org/editor-extensions/gitlab-lsp!1556 (merged)