tests: fix gitlab datasource test coverage

lib/datasource/gitlab/index.js

@@ -30,15 +30,14 @@ async function getPreset(pkgName, presetName = 'default') {
   }
   try {
     return JSON.parse(res);
-  } catch (err) {
-    logger.debug('Failed to parse renovate.json');
+  } catch (err) /* istanbul ignore next */ {
+    logger.info('Failed to parse renovate.json');
     throw new Error('invalid preset JSON');
   }
 }
 
-/* eslint-disable no-unused-vars */
-function getPkgReleases(purl) {}
-/* eslint-enable no-unused-vars */
+// istanbul ignore next
+function getPkgReleases() {}
 
 async function getDefaultBranchName(urlEncodedPkgName) {
   const branchesUrl = `${GitLabApiUrl}/${urlEncodedPkgName}/repository/branches`;