Bump Cert-manager version in installation documentation

[github-actions]

Bump Cert-manager version in installation documentation

docs: update cert-manager referenced version v1.20.2

2 file(s) updated with "https://github.com/cert-manager/cert-manager/releases/download/v1.20.2/": * docs/installation/other_inst_scenarios/install_epinio_on_rancher_desktop.md * docs/tutorials/single-dev-workflow.md

v1.20.2

v1.20.2 fixes invalid YAML generated in the Helm chart when both `webhook.config`
and `webhook.volumes` are defined, and bumps Go to 1.26.2 along with dependencies
to address reported vulnerabilities.

## Changes by Kind

### Bug or Regression

- Helm: Fix invalid YAML generated when both `webhook.config` and `webhook.volumes` are defined. (#8665, @cert-manager-bot)

### Other (Cleanup or Flake)

- Bump go dependencies with reported vulnerabilities (#8704, @erikgb)
- Bump go to 1.26.2 (#8703, @erikgb)

v1.20.1

v1.20.1 fixes an issue for OpenShift users that has to do with the finalizer RBAC, bumps gRPC to address a reported non-affecting vulnerability, and fixes a duplicate `parentRef` bug when both issuer config and annotations are present (Gateway API).

### Bug or Regression

- Fixed duplicate `parentRef` bug when both issuer config and annotations are present. (#8658, @hjoshi123)
- Add missing issuer finalizer RBAC to the order controller to support owner references. This was preventing OpenShift users from being able to upgrade to v1.20.0. (#8655, @erikgb)
- Bump google.golang.org/grpc to fix vulnerability reported by scanners. This isn't a vulnerability that affects cert-manager, but we are bumping it because it is reported by scanners. (#8657, @erikgb)

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