techdocs-backend: update Gitlab clone auth

.changeset/famous-items-travel.md

@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-techdocs-backend': patch
+---
+
+Update URL auth format for Gitlab clone

plugins/techdocs-backend/src/helpers.ts

@@ -146,8 +146,18 @@ export const checkoutGitRepository = async (
 
   if (token) {
     const type = getGitRepoType(repoUrl);
-    const auth = type === 'github' ? `${token}:x-oauth-basic` : `:${token}`;
-    parsedGitLocation.token = auth;
+    switch (type) {
+      case 'gitlab':
+        // Personal Access Token
+        parsedGitLocation.token = `dummyUsername:${token}`;
+        parsedGitLocation.git_suffix = true;
+        break;
+      case 'github':
+        parsedGitLocation.token = `${token}:x-oauth-basic`;
+        break;
+      default:
+        parsedGitLocation.token = `:${token}`;
+    }
   }
 
   const repositoryCheckoutUrl = parsedGitLocation.toString('https');