message: catalog-backend: use assertError
diff: import { UrlReader } from '@backstage/backend-common';
  import { Entity, LocationSpec } from '@backstage/catalog-model';
  +import { assertError } from '@backstage/errors';
  import parseGitUrl from 'git-url-parse';
  import limiterFactory from 'p-limit';
  import { Logger } from 'winston';
  @@ -91,6 +92,7 @@ export class UrlReaderProcessor implements CatalogProcessor {
  });
  }
  } catch (error) {
  + assertError(error);
  const message = `Unable to read ${location.type}, ${error}`;
  if (error.name === 'NotModifiedError' && cacheItem) {
  for (const parseResult of cacheItem.value) {
  