docs: document test coverage for release branches

Signed-off-by: Stefan Büringer buringerst@vmware.com

CONTRIBUTING.md

@@ -145,8 +145,10 @@ Cluster API maintains the most recent release/releases for all supported API and
 | **v1alpha4** | EOL since 2022-04-06 |
 | **v1alpha3** | EOL since 2022-02-23 |
 
-- For the latest API version we support the two most recent minor releases; older minor releases are immediately unsupported when a new major/minor release is available. 
+- For the current stable API version (v1beta1) we support the two most recent minor releases; older minor releases are immediately unsupported when a new major/minor release is available.
 - For older API versions we only support the most recent minor release until the API version reaches EOL.
+- We will maintain test coverage for all supported minor releases and for one additional release for the current stable API version in case we have to do an emergency patch release.
+  For example, if v1.2 and v1.3 are currently supported, we will also maintain test coverage for v1.1 for one additional release cycle. When v1.4 is released, tests for v1.1 will be removed.
 
 | Minor Release | API Version  | Supported Until                                      |
 |---------------|--------------|------------------------------------------------------|

docs/release/release-tasks.md

@@ -387,6 +387,7 @@ Stakeholders are: (TBD)
 #### Setup jobs and dashboards for a new release branch
 
 The goal of this task is to have test coverage for the new release branch and results in testgrid.
+While we add test coverage for the new release branch we will also drop the tests for old release branches if necessary.
 
 1. Create new jobs based on the jobs running against our `main` branch:
     1. Copy `config/jobs/kubernetes-sigs/cluster-api/cluster-api-periodics-main.yaml` to `config/jobs/kubernetes-sigs/cluster-api/cluster-api-periodics-release-1-4.yaml`.
@@ -401,7 +402,9 @@ The goal of this task is to have test coverage for the new release branch and re
             * Change interval (let's use the same as for `1.3`).
         5. For presubmits additionally: Adjust branches: `^main$` => `^release-1.4$`.
 2. Create a new dashboard for the new branch in: `test-infra/config/testgrids/kubernetes/sig-cluster-lifecycle/config.yaml` (`dashboard_groups` and `dashboards`).
-3. Verify the jobs and dashboards a day later by taking a look at: `https://testgrid.k8s.io/sig-cluster-lifecycle-cluster-api-1.4`
+3. Remove tests for old release branches according to our policy documented in [Support and guarantees](../../CONTRIBUTING.md#support-and-guarantees)
+   For example, let's assume we just created tests for v1.4, then we can now drop test coverage for the release-1.1 branch.
+4. Verify the jobs and dashboards a day later by taking a look at: `https://testgrid.k8s.io/sig-cluster-lifecycle-cluster-api-1.4`
 
 Prior art: [Add jobs for CAPI release 1.2](https://github.com/kubernetes/test-infra/pull/26621)