chore: fix mergify auto-approve label (backport #197) (#201)

This is an automatic backport of pull request #197 done by [Mergify](https://mergify.com).
Cherry-pick of dc8b3b3 has failed:
```
On branch mergify/bp/kubectl-v25/main/pr-197
Your branch is up to date with 'origin/kubectl-v25/main'.

You are currently cherry-picking commit dc8b3b3.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   .projenrc.ts

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   .mergify.yml

```


To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/github/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

---


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.projenrc.ts

@@ -59,9 +59,7 @@ const project = new awscdk.AwsCdkConstructLibrary({
         actions: {
           backport: {
             regexes: [`kubectl-v(?!20|${SPEC_VERSION})[\\d]*\\/main`],
-          },
-          label: {
-            add: ['auto-approve'],
+            labels: ['auto-approve'],
           },
         },
       }],