fix link

Author: shecodesmagic

docs/release/role-handbooks/ci-signal/README.md

@@ -89,7 +89,7 @@ To reduce the amount of flakes please periodically:
 ### Post-release cleanup
 Once the new minor release (e.g., `v1.8.0`) has been officially cut, perform the following cleanup:
 
-- Remove old release branches and unused versions from the `cluster-api-prowjob-gen.yaml` file in [test-infra](https://github.com/kubernetes/test-infra/blob/master/config/jobs/kubernetes-sigs/cluster-api/) according to our policy documented in [Support and guarantees](../../book/src/reference/versions.md#cluster-api-release-vs-api-versions)
+- Remove old release branches and unused versions from the `cluster-api-prowjob-gen.yaml` file in [test-infra](https://github.com/kubernetes/test-infra/blob/master/config/jobs/kubernetes-sigs/cluster-api/) according to our policy documented in [Support and guarantees](../../../book/src/reference/versions.md#cluster-api-release-vs-api-versions)
 
 We can now drop test coverage for branches out of support (e.g. `release-1.5`).