feat: add fingerprint to old branches (#17393)

lib/workers/repository/process/write.spec.ts

@@ -120,7 +120,13 @@ describe('workers/repository/process/write', () => {
         },
       ]);
       repoCache.getCache.mockReturnValueOnce({
-        branches: [{ branchName: 'new/some-branch' } as BranchCache],
+        branches: [
+          {
+            branchName: 'new/some-branch',
+            sha: '111',
+            branchFingerprint: '111',
+          } as BranchCache,
+        ],
       });
       branchWorker.processBranch.mockResolvedValueOnce({
         branchExists: true,

lib/workers/repository/process/write.ts

@@ -96,9 +96,10 @@ export async function writeUpdates(
     branch.prBlockedBy = res?.prBlockedBy;
     branch.prNo = res?.prNo;
     branch.result = res?.result;
-    branch.branchFingerprint = res?.commitSha
-      ? branchFingerprint
-      : branchCache.branchFingerprint;
+    branch.branchFingerprint =
+      res?.commitSha || !branchCache.branchFingerprint
+        ? branchFingerprint
+        : branchCache.branchFingerprint;
 
     if (
       branch.result === BranchResult.Automerged &&