Update Kube Versions for envtest-existing & kuttl PR Checks

Updates the min/max versions of Kubernetes used by the kubernetes-k3d
and kuttl-k3d PR checks.  This means PR checks for envtest-existing and
kuttl tests are now run against the current min/max versions of Kubernetes
supported by PGO according to the Supported Platforms page in the docs.

Author: sfc-gh-alecuyer

.github/workflows/test.yaml

@@ -58,7 +58,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        kubernetes: [v1.31, v1.28]
+        kubernetes: [v1.33, v1.28]
     steps:
       - uses: actions/checkout@v4
       - uses: actions/setup-go@v5
@@ -92,7 +92,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        kubernetes: [v1.32, v1.31, v1.30, v1.29, v1.28]
+        kubernetes: [v1.33, v1.28]
     steps:
       - uses: actions/checkout@v4
       - uses: actions/setup-go@v5