Update min kubernetes version in the install doc

v0.61.0 updated the minimum version of Kubernetes to 1.28.

Update the docs to reflect this so the website has the correct content.

Author: AlanGreene

docs/install.md

@@ -21,7 +21,7 @@ This guide explains how to install Tekton Pipelines.
 
 ## Prerequisites
 
--   A [Kubernetes cluster][k8s] running version 1.25 or later.
+-   A [Kubernetes cluster][k8s] running version 1.28 or later.
 -   [Kubectl][].
 -   Grant `cluster-admin` privileges to the current user. See the [Kubernetes
     role-based access control (RBAC) docs][rbac] for more information.